Download California Red-Legged Frog (Rana aurora draytonii)

AMPHIBIANS
California Red-Legged Frog (Rana aurora draytonii)
California Red-Legged Frog (Rana aurora draytonii)
Status
State:
Species of Special Concern
Federal:
Threatened
Critical Habitat:
Critical habitat for California red-legged frog was
established by U.S. Fish and Wildlife Service in a final
rule on April 13, 2006 (71 FR 19243). Revised critical
habitat was designated March 2010 (75 FR 12816).
Critical habitat is present in the study area.
Range
The historical range of the California red-legged frog (Rana aurora draytonii)
extended along the coast from the vicinity of Point Reyes National Seashore,
Marin County, California and inland from Redding, Shasta County southward to
northwestern Baja California, Mexico (Jennings and Hayes 1985; Hayes and
Krempels 1986). The current distribution of this subspecies includes isolated
localities in the Sierra Nevada, northern Coast, and Northern Traverse Ranges. It
is still common in the San Francisco Bay area and along the central coast. It is
now believed to be extirpated from the southern Traverse and Peninsular ranges
(U.S. Fish and Wildlife Service 2002) (Figure 1).
Occurrences within the HCP Study Area
Contra Costa and Alameda Counties contain the majority of known California
red-legged frog occurrences in the San Francisco Bay Area (U.S. Fish and
Wildlife Service 2002). However, this subspecies seems to have been nearly
eliminated from the western lowland portions of these counties, particularly near
urbanization. Figure 1 depicts where the habitat conservation plan (HCP) study
area occurs in relation to the current distribution of the California red-legged
frog.
The land cover map developed for the HCP study area identifies over 150 ponds,
many of which are known or potential habitat for this subspecies. According to
the California Natural Diversity Database (CNDDB), 18 occurrences of
California red-legged frog have been documented within the study area
(California Natural Diversity Database 2008). Adult frogs have been observed in
Upper Alameda Creek in the Sunol Regional Wilderness (Bobzien and DiDonato
2007), and in many creeks from this area, south to Henry Coe State Park
(U.S. Fish and Wildlife Service 2002). In 2002, the San Francisco Public Utilities
Commission (SFPUC) conducted protocol-level surveys for frogs in aquatic
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
1
AMPHIBIANS
California Red-Legged Frog (Rana aurora draytonii)
habitat near Niles and Sunol Dams. More than a dozen California red-legged
frogs were observed in a pond north of Sunol Dam (next to the access road);
however, no red-legged frogs were observed in the vicinity of Niles Dam
(San Francisco Public Utilities Commission 2003). More recently, California
red-legged frogs were observed in wetland and pond habitats within the Alameda
Siphon No. 4 Project Area along the Alameda Creek riparian zone downstream
of Welch Creek. (Dettman and Weinberg, CNDDB submissions and SFPUC
monitoring reports 2010.)
The U.S. Fish and Wildlife Service (USFWS) established eight recovery units
distributed throughout portions of historic and current range for this subspecies.
The purpose of these units is to meet different recovery strategies based on
regional populations and threats. The HCP study area falls within the South and
East San Francisco Bay Recovery Unit for California red-legged frog (U.S. Fish
and Wildlife Service 2002). Within each recovery unit, USFWS identified core
areas where recovery actions will be focused. East San Francisco Bay, which
includes the Alameda watershed, has been identified as one of these core areas.
This core area was chosen because it is currently occupied and is considered a
source population that maintains connectivity with other populations. Hence,
protection and management of the Alameda watershed would promote the
recovery of California red-legged frog by protecting occupied core habitat of a
source population and promoting the long-term viability of the species.
Revised critical habitat for this species was designated in March 2010
(75 FR 12816) by the USFWS. Within the HCP study area, there is a total of
33,998 acres of critical habitat, with 32,752 acres in ALA-2, 1,109 acres in
CCS-2B, and 137 acres in STC-1.
Biology
Habitat
Within their range, California red-legged frogs occur from sea level to about
5,000 feet above sea level (U.S. Fish and Wildlife Service 2002; Stebbins 2003).
Almost all of the documented occurrences of this subspecies, however, are
located below 3,500 feet (U.S. Fish and Wildlife Service 2002). Breeding sites
include a variety of aquatic habitats—larvae, tadpoles and metamorphs use
streams, deep pools, backwaters within streams and creeks, ponds, marshes, sag
ponds, dune ponds, and lagoons. Breeding adults are commonly found in deep
(more than two feet), still, or slow-moving water with dense, shrubby riparian or
emergent vegetation (Hayes and Jennings 1988). Adult frogs have also been
observed in shallow sections of streams that are not shrouded by riparian
vegetation. Generally, streams with high flows and cold temperatures in spring
are unsuitable for eggs and tadpoles. Stock ponds are frequently used by this
subspecies if they are managed to provide suitable hydroperiod, pond structure,
vegetative cover, and control of nonnative predators, especially bullfrogs.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
2
AMPHIBIANS
California Red-Legged Frog (Rana aurora draytonii)
During dry periods, California red-legged frogs are seldom found far from water.
However, during wet weather, individuals may make overland excursions
through upland habitats over distances up to two miles. These dispersal
movements generally follow straight-line, point-to-point migrations rather than
specific habitat corridors. Dispersal distances are believed to depend on the
availability of suitable habitat and prevailing environmental conditions though
very little is known about how California red-legged frogs use upland habitats
during dispersal.
During summer, California red-legged frogs often disperse from their breeding
habitat to forage and seek summer (aestivation) habitat if water is not available
(U.S. Fish and Wildlife Service 2002). This habitat may include shelter under
boulders, rocks, logs, industrial debris, agricultural drains, watering troughs,
abandoned sheds, or hay-ricks. They will also use small mammal burrows,
incised stream channels, or areas with moist leaf litter (Jennings and Hayes 1994;
U.S. Fish and Wildlife Service 1996, 2002). This summer movement behavior,
however, has not been observed in all California red-legged frog populations
studied.
Foraging Requirements
California red-legged frogs consume a wide variety of prey. Adult frogs typically
feed on aquatic and terrestrial insects, crustaceans and snails (Stebbins 2003;
Hayes and Tennant 1985), as well as worms, fish, tadpoles, smaller frogs
(e.g., Pseudacris regilla), and occasionally mice (Peromyscus californicus)
(U.S. Fish and Wildlife Service 2002). Aquatic larvae are mostly herbivorous
algae grazers (Jennings et al. 1992). Feeding generally occurs along the shoreline
of ponds or other watercourses and on the water surface. Juveniles appear to
forage during both daytime and nighttime, whereas subadults and adults tend to
feed more exclusively at night (Hayes and Tennant 1985).
Reproduction
California red-legged frogs breed from November through April (Storer 1925;
U.S. Fish and Wildlife Service 2002). Males usually appear at the breeding sites
2 to 4 weeks before females. Females are attracted to calling males. Females lay
egg masses containing about 2,000 to 5,000 eggs, which hatch in 6 to 14 days,
depending on water temperatures (U.S. Fish and Wildlife Service 2002). Larvae
metamorphose in 3.5 to 7 months, typically between July and September (Storer
1925; Wright and Wright 1949; U.S. Fish and Wildlife Service 2002). Sexual
maturity is usually attained by males at two years of age and females at three
years of age.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
3
AMPHIBIANS
California Red-Legged Frog (Rana aurora draytonii)
Demography
Adult California red-legged frogs can live 8 to 10 years (Jennings et al. 1992),
but the average life span is probably much lower (Scott pers. comm. in U.S. Fish
and Wildlife Service 2002). Most mortality occurs during the tadpole stage (Licht
1974). No long-term studies have been conducted on the population dynamics of
red-legged frogs.
Ecological Relationships
California red-legged frogs are primary, secondary, and tertiary consumers in the
aquatic/terrestrial food web of their habitat. As described above, they prey on a
variety of invertebrates and vertebrates, as well as algae as larvae. Numerous
native predators prey on these frogs, including raccoons (Procyon lotor), great
blue herons (Ardea herodias), American bitterns (Botaurus lentiginosus), blackcrowned night herons (Nycticorax nycticorax), red-shouldered hawks (Buteo
lineatus), opossums (Didelphis virginiana), striped skunks (Mephitis mephitis),
spotted skunks (Spilogale putorius), and garter snakes (Thamnophis spp.) (Fitch
1940; Fox 1952; Jennings and Hayes 1990; Rathbun and Murphy 1996). In some
areas, introduced aquatic vertebrates and invertebrates also prey on one or more
of the life stages of California red-legged frogs. These predators include bullfrogs
(Rana catesbeiana), African clawed frogs (Xenopus laevis), red swamp crayfish
(Procambarus clarkii), signal crayfish (Pacifastacus leniusculus), bass
(Micropterus spp.), catfish (Ictalurus spp.), sunfish (Lepomis spp.), and
mosquitofish (Gambusia affinis) (Hayes and Jennings 1986).
Population Trend
Global:
State endemic; declining
State:
Declining
Within HCP Apparently stable in some areas
Study Area:
Threats and Reasons for Decline
Although population numbers are not precisely known, the USFWS estimates
that California red-legged frog populations are declining at a rapid rate. A 70%
reduction in the geographic range of this subspecies was witnessed in the early to
mid-1990s. This decline was primarily a result of habitat loss and alteration,
over-exploitation for human food, and introduction of exotic predators (U.S. Fish
and Wildlife Service 2003).
The viability of existing California red-legged frog populations is threatened by
numerous human activities that often act synergistically and cumulatively with
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
4
AMPHIBIANS
California Red-Legged Frog (Rana aurora draytonii)
natural disturbances (i.e., droughts or floods) (U.S. Fish and Wildlife Service
2002). These activities include the degradation, fragmentation, and loss of habitat
through agriculture, urbanization, mining, overgrazing, recreation, timber
harvesting, nonnative plants, impoundments, water diversions, degraded water
quality, and introduced predators.
Habitat along many stream courses has been isolated and fragmented, resulting in
reduced connectivity between populations and lowered dispersal opportunities.
These isolated populations are now more vulnerable to extinction through
stochastic environmental events (i.e., drought, floods) and human-caused impacts
(i.e., grazing disturbance, contaminant spills) (Soulé 1998). In a comprehensive
evaluation of prevailing hypotheses on the causes of declines in the California
red-legged frog populations, Davidson et al. (2001) determined that there is a
strong statistical correlation between locations where frog numbers had declined
and upwind agricultural land use. They concluded that wind-borne agrochemicals
might be an important factor in these declines.
Poorly managed recreation, mining, timber harvest, and infrastructure
maintenance activities, such as road construction and repair, trail development
and facilities development, can also have significant detrimental effects on
remaining California red-legged habitat through disturbance, contamination, and
introduction of nonnative species that prey on or compete with the frogs.
Within the Alameda watershed, direct impacts on California red-legged frog
could result from activities that occur in either breeding or upland habitats. Such
activities include fence installation and maintenance, road use, reservoir
management, watershed pipeline maintenance, and HCP fishery management
releases. Impacts on breeding habitats from fence repair and installation and from
pipeline maintenance would occur at locations where fencing crosses existing
ponds or wetlands. Impacts from reservoir releases could alter aquatic habitat or
existing hydrologic regimes. Direct impacts on potential California red-legged
frog aquatic breeding habitat from scheduled releases for instream flows could
occur due to reduced flows from November through May. Such reductions could
result in narrower stream widths downstream of Calaveras and San Antonio
Dams during the breeding period, which could cause desiccation of egg masses
and mortality in Calaveras, San Antonio, and Alameda Creeks. However, these
streams generally support higher spring flows, which are generally unsuitable for
eggs and tadpoles (Stebbins 1985; Hayes and Jennings 1988). Therefore, it is
likely that breeding in these streams is already limited and that impacts would be
low or even nonexistent. These streams also represent only a portion of the
available habitat for California red-legged frog in the study area; thus, direct
impacts on potential California red-legged frog aquatic breeding habitat from
scheduled releases for instream flows would be minimized. Threats to the
California red-legged frog habitat also include invasion of nonnative species.
Upper Alameda Creek and other drainages in the Sunol Regional Wilderness
have been identified as areas in need of nonnative predator control. In addition,
ponds within the HCP study area contain nonnative predators (e.g., bullfrog and
bass). Studies indicate that fewer than 5% of California red-legged frogs will
survive in ponds with bullfrogs (Lawler et al. 1999).
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
5
AMPHIBIANS
California Red-Legged Frog (Rana aurora draytonii)
Upland habitats could be affected to a small degree by almost all covered
activities. The largest impacts would be from road construction, bridge
replacement/construction, fence and gate repair and installation, vegetation
management, recreation on lands owned by the SFPUC, high-traffic grazing
areas, and pipeline maintenance. These activities would affect upland habitats
such as nonnative grasslands that are used by this species. Construction of roads
and bridges would result in permanent impacts; however, the remaining activities
would have only temporary impacts and not result in loss of habitat. Because the
activities would occur for discrete periods of time in specific locations, individual
covered species would likely utilize alternative upland sites for the duration of
the temporary covered activity resulting in negligible impacts to the species.
Because amphibians require both terrestrial and aquatic environments, and
because they migrate between two habitat types, they can be particularly
sensitive to the effect of changes that permanently alter either of these
environments. New roads can reduce successful movement between aquatic and
terrestrial habitat.
Livestock grazing may decrease suitability of riparian habitat for California redlegged frog populations within the HCP study area. Cattle degrade riparian
habitat because they congregate in these areas and trample riparian vegetation.
This loss of streamside and pond-margin vegetation can result in increased
erosion, increased water temperatures, and reduced numbers of available prey
such as insects and small mammals. Conversely, in some grazing areas,
artificially created stock ponds provide ideal breeding habitat for California redlegged frog, and grazing may help maintain pond suitability by keeping ponds
from being choked with vegetation (U.S. Fish and Wildlife Service 2002).
Finally, gravel mining can degrade habitat by altering hydrology of aquatic
systems, increasing sedimentation, and degrading water quality. The USFWS
recommends elimination of mining activities in core watersheds where California
red-legged frogs are threatened by such activities (U.S. Fish and Wildlife Service
2002).
The recovery plan for the California red-legged frog (U.S. Fish and Wildlife
Service 2002) recommends implementing the following conservation measures in
the East San Francisco Bay core area.

Protect existing populations.

Control non-native predators.

Study effects of grazing in riparian corridors, ponds, and uplands (e.g., on
East Bay Regional Park District Lands).

Reduce impacts associated with livestock grazing.

Protect habitat connectivity.

Minimize effects of recreation and off-road vehicle use (e.g., Corral Hollow
watershed).

Avoid and reduce impacts of urbanization.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
6
AMPHIBIANS
California Red-Legged Frog (Rana aurora draytonii)

Protect habitat buffers from nearby urbanization.
Data Characterization
A moderate amount of literature is available regarding the California red-legged
frog because of its threatened status and the recent trend in global decline in
amphibians. Most of the literature pertains to habitat requirements, population
trends, ecological relationships, threats, and conservation efforts.
This subspecies has been included in numerous regional HCPs in California
(e.g., Wilder Quarry, Kern Water Bank, East Contra Costa County). The
available data, as summarized in this subspecies profile, are adequate to evaluate
impacts on this subspecies, develop conservation measures, and develop
monitoring protocols. Data gaps include lack of knowledge about presence of
non-native predators and the extent of livestock grazing impacts on frog habitat
within the Alameda watershed. If non-native predators are identified as a threat
within the HCP study area, potential and known breeding sites of non-native
predators should be eliminated. Methods such as dewatering stock ponds with
known populations of nonnative predators at regular intervals (e.g., annually or
bi-annually) will achieve this goal (U.S. Fish and Wildlife Service 2002).
Additionally, research is necessary to understand optimum livestock grazing
regimes (e.g., rest rotation and deferred utilization) for California red-legged frog
habitat. According to USFWS (2002), opportunities exist to manage grazed lands
in a manner that reduces impacts to frog habitat.
Modeled Species Distribution in HCP Study Area
Figure 2 shows the habitat distribution model for the California red-legged frog
within the 46,700-acre study area.
Model Description
Model Assumptions
1. Ponds and streams in valley needlegrass, grassland, non-native grassland,
serpentine bunchgrass grassland, mixed evergreen forest/oak woodland,
valley oak woodland, blue oak woodland, oak savanna, central coast live oak
riparian forest, coast live oak riparian forest, sycamore alluvial woodland,
willow riparian forest/scrub, white alder riparian forest, freshwater marsh,
freshwater seep, Diablan sage scrub and cultivated agriculture land-cover
types were considered suitable breeding habitat for California red-legged
frog.
2. Streams in urban/developed, nursery, and turf areas were also considered
suitable breeding habitat for this species.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
7
AMPHIBIANS
California Red-Legged Frog (Rana aurora draytonii)
3. Ponds in urban/developed, nursery, and turf areas with substantial areas of
suitable aestivation habitat intact (>50% of 1-mile buffer) were considered to
be suitable breeding habitat.
4. All non-aquatic land-cover types, except urban/developed and nursery,
within 1 mile of potential breeding sites were considered potential dispersal
and summer aestivation habitat for this species.
Rationale
Breeding habitat: Breeding sites used by California red-legged frogs include a
variety of aquatic habitats (Stebbins 2003; Hayes and Jennings 1988; U.S. Fish
and Wildlife Service 2002). Within the HCP study area stock ponds are
frequently used as breeding sites by this species if the ponds are managed to
provide suitable hydroperiod, pond structure, vegetative cover, and control of
nonnative predators. All ponds surveyed were considered suitable habitat for
California red-legged frogs. Although periodic drought can enhance pond
suitability by eliminating bullfrogs, suitability ranking of ponds that were dry in
September was reduced from a 2 to 1. Due to the limitations of our 1-season
pond survey it is unknown whether these ponds dry annually or periodically,
therefore the increased suitability of pond breeding habitat due to periodic
drought could not be determined.
Dispersal and upland summer habitat: Movements of up to 1 mile from
breeding sites to other breeding sites during the wet season and from rapidly
drying breeding sites to summer upland sites are apparently typical (Stebbins
2003; U.S. Fish and Wildlife Service 2002), although some individual frogs have
been found to achieve dispersal distances of up to 2 miles (U.S. Fish and Wildlife
Service 2002). These dispersal movements may be along long-established
historic dispersal corridors that provide specific sensory cues that guide the
seasonal movement of the frogs (Stebbins 2003). Dispersal distances are believed
to depend on the availability of suitable habitat and prevailing environmental
conditions. However, because the actual movement patterns of California redlegged frogs in these habitats is generally not known, for this model we
conservatively estimated that all non-urban land cover areas within a radius of
1 mile from all potential breeding sites were potential dispersal and/or upland
habitats for California red-legged frogs.
Model Results
Within the entire study area there are 993 acres of modeled breeding habitat (and
31,039 acres of modeled potential migration and aestivation habitat for this
species.
Results of the habitat distribution model are based on two tiers of analysis. The
first tier of analysis is based on application of the assumptions provided above
using geographic information systems (GIS). Using this analysis none of pond
habitat was found to be unsuitable breeding habitat for the California red-legged
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
8
AMPHIBIANS
California Red-Legged Frog (Rana aurora draytonii)
frog. Thus, all ponds in the HCP study area were subject to the second tier of
analysis. The second tier of analysis involved application of data derived from
field surveys of 68 ponds within the study area.
Biologists conducted the pond survey in September 2003. The purpose of this
survey was to provide both physical and biological data to assess and rank each
surveyed pond for breeding habitat suitability. Of the surveyed ponds, 100%
were considered suitable breeding habitat. Suitable ponds were then ranked as
having high suitability (given a score of 2) or low suitability (given a score of 1)
depending on presence of water and/or predators. Based on these characteristics,
18% of the ponds were considered highly suitable breeding habitat while 82% of
the ponds were considered moderately suitable breeding habitat (Figure 2).
The final step in the second tier of analysis was to extrapolate the findings from
the pond survey (68 pond sample) to all ponds in the study area considered
suitable after the first tier of analysis. The goal of the extrapolation was to
determine the acres of suitable pond breeding habitat in the study area based on
the results of our pond survey. For the California red-legged frog our analysis
indicates that 100% of the surveyed ponds contain suitable breeding habitat. (For
the extrapolation, all ponds receiving a score of 1 or 2 were considered suitable
breeding habitat.) The result of this analysis is a total of 993 acres of modeled
breeding habitat comprised of 36 acres of pond habitat and 957 acres of stream
and upland habitat.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
9
HCP Study Area
Breeding Range
0
100
MILES
FIGURE 1
California Red-Legged Frog (Rana aurora draytonii)
Distribution
Source: Adapted USFWS 2002 Recovery Plan for the CRLF.
Figure 2 Habitat Distribution Model for California Red Legged Frog (Rana aurora draytonii)
Legend
Surveyed Ponds
oa
Sunol
d
Ala
il
th
l R
ou
te
!
(
!
(
Valleci to
's C
re
!
(
!
(
!
(
ir
vo
er as
Calav
Re
s
o
!
(
!
(
!
(
!
(
Potential Migration and Aestivation Habitat
h
!
(
lc
!
(
Known Occurence
!
(
!
(
!
( !
(
!
(
!
(
Stream
!
(
!
(
In
!
(!
(
(!
on
!
(
k
!
(
!
(
ee
Cr
e !(
rs
n
p
h C
re e k
dia
ad
n
Hay h
c
Gul
!
(
!
(
!
(
!
((
! !
(
k
Ro
Fremont
We
lc
p
!
(
e
Cr e
ri d a n
A
s
u
!
(
!
(
!
(!
(
!
!
((
!
(
es
a
os t
S he
!
(
(Note: Core Breeding Habitat in
ponds cannot be seen at
this scale, and are overwritten
by Pond Habitat Suitablity points.)
G
!
(
Unsurveyed pond
Suitable Breeding Habitat
m
!
(
!
(
!
(
!
(
!
(
ia
!
(
!
(
(
!!
(
ill
!
(!
(
!
(
!
(
!
(
!
(
!
(
!
(
!
( !
(
!
(
W
k
!
(
!
(
!
(
!
(
!
(
!
(
!
(
!
(
Pond Habitat Suitability = Not Suitable
Va
lle
!
(
!
(
Cr
ee
!
(
!
( (
!
! (
!
(
!
(
!
(
!
(
!
(
!
(
!
(
(
!!
(
!
(
(
!
( !
!
(!
(
i
!
(
!
(
n A
C
La
!
(
to n
Sa
!
(
y
!
(
S
n
an A
!
(
lle
!
(
!
(
!
(
Road
80
Va
I
!
(
Pond Habitat Suitability = Moderate
De
l
!
(
!
(
io
!
(
!
(
!
(
n
nto
!
(
nol
-6
( !
!
(!
(
Su
!
(
!
(
!
(
!
((
!!
(
!
(
(
!
(!
!
(
!
(
!
(
eek
!
(
Unsurveyed Ponds
ek
!
( !
(
!
(
/ R
er
a
Cr
ad
!
(
ed
!
(
Ro
!
(
!
(
m
!
(
(!
(
!!
(
Fo o
i le
N
R
V
c ito s
a lle
Pond Habitat Suitability = High
84
ke
La
s
Ca n y on
l
guna
o de a L a
d
r oy
80
I- 6
Ar
!
(
Primary Road
Reservoir
Secondary Road
Study Area
County Line
R
!
(
id
SFPUC Ownership
g
en
yd
Le
Cr
k
ee
(
!
(!
!
(
!
(
e
!
(
!
(
!
(
A lame
d a Cr
ee
k
(
!!
(
!
(
©
!
(
!
(
Oa
!
(
la
Ca
I - 68
ll er
0
We
0
I-88
ve
Re
Ro ad
!
(
se
rv o
!
(
!
(
!
(
!
(
P
!
(
!
(
oa
h R
rt
!
(
!
(
!
(
!
(
Ho
ve
yo
o
!
(
d
Ma rs
y
nd
o
!
(
0.5
1
2
Miles
1:108,657
!
(
g
Calav
er
e
as
Cre
!
(
!
(
ek
!
(
!
(
!
(
Mt.
Day
!
(
!
(
5/6/08
0
!
(
R
!
(
id
!
(
!
(
!
(
d
Santa Clara Co.
ro
Ar
ras R o a d
R oa
Alameda Co.
d g !(
!
( e
ir
Cal a ve
er
F elt
Ri
ra s
!
(
Milpitas
k
AMPHIBIANS
California Tiger Salamander (Ambystoma californiense)
California Tiger Salamander
(Ambystoma californiense)
Status
State:
Threatened (California Department of Fish and Game 2010)1
Federal:
Central California population listed as Threatened (U.S. Fish
and Wildlife Service 2004); Sonoma County and Santa
Barbara County populations listed as Endangered (U.S. Fish
and Wildlife Service 2000, 2003)2
Critical Habitat: Designated for the central California population only on
August 23, 2005 (70 FR 49379); Proposed rule for Sonoma
County population published on August 18, 2009 (74 FR
41662)
Range
The California tiger salamander (Ambystoma californiense) is endemic to
California. Historically, the California tiger salamander probably occurred in
grassland habitats throughout much of the state, but habitat conversion has
reduced the species’ range and decreased breeding populations (Stebbins 2003).
Currently, the California tiger salamander occurs in six populations in the Central
Valley and Sierra Nevada foothills from Yolo County south to Tulare County,
and in the coastal valleys and foothills from Sonoma County south to Santa
Barbara County (California Wildlife Habitat Relationships 2005) (Figure 1).
The six populations of California tiger salamander are found in Sonoma County,
Santa Barbara County, the Bay Area (central and southern Alameda County,
Santa Clara County, western Stanislaus and Merced Counties, and San Benito
County), the Central Valley (Yolo County, Sacramento County, East Contra
Costa County, northeast Alameda County, San Joaquin County, Stanislaus
County, Merced County and northwest Madera County), southern San Joaquin
Valley (Madera County, central Fresno County, northern Tulare County, and
Kings County), and the Central Coast Range (south Santa Cruz County,
Monterey County, northern San Luis Obispo County, western San Benito, Fresno
and Kern Counties) (U.S. Fish and Wildlife Service 2003). Isolated populations
1
2
The California Fish and Game Commission determined that the California tiger salamander should be listed as
threatened on May 20, 2010. This determination still needs to be finalized by the State Office of Administrative
Law. The state listing applies to the entire range of this species.
The 2004 listing of the central California population of the California tiger salamander (U.S. Fish and Wildlife
Service 2004) also downgraded the Sonoma County and Santa Barbara County populations of the species from
endangered to threatened. However, an August 19, 2005 ruling from U.S. District Judge William Alsup vacated
this downlisting, so these populations remain listed as endangered.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
1
AMPHIBIANS
California Tiger Salamander (Ambystoma californiense)
are found at the Gray’s Lodge Wildlife Area in Butte County and at Grass Lake
in Siskiyou County (California Wildlife Habitat Relationships 2005).
Occurrences within the HCP Study Area
Because a comprehensive survey for the California tiger salamander has not been
conducted in the HCP study area, neither the current population size nor the
locations of all occurrences are known. However, this species has been observed
in numerous ponds throughout the HCP study area (Koopman pers. comm.). The
California Natural Diversity Database (CNDDB) (2008) records for the area
document 106 occurrences of California tiger salamander from 1961 to 2001 and
24 occurrences within the HCP study area (California Natural Diversity Database
2008).
Critical habitat was finalized for the central population (the population in the
HCP study area) on August 23, 2005 (70 FR 49379). The East Bay Critical
Habitat Unit 3 falls completely within the HCP study area. This unit comprises
619 acres and is located just east of Calaveras Reservoir, adjacent to and south of
the Arroyo Hondo arm of the reservoir. In addition, 5% (150 acres) of East Bay
Critical Habitat Unit 5 also falls in the study area.
Biology
Habitat
Both aquatic and terrestrial habitats are important elements for long-term
California tiger salamander survival (California Department of Fish and Game
2010). A key requirement for California tiger salamander long-term population
viability is large areas of intact upland habitat surrounding breeding sites
(Trenham and Shaffer 2005; Searcy and Shaffer 2008; California Department of
Fish and Game 2010). In addition, intact terrestrial habitat for movement
between adjacent breeding sites across intact terrestrial habitat is a key factor in
population viability (California Department of Fish and Game 2010).
California tiger salamander is a lowland species restricted to grasslands and low
foothill regions where its breeding habitat (long-lasting rain pools) occurs. In
addition to temporary ponds or pools, California tiger salamanders also breed in
slower portions of streams and in some permanent waters (Stebbins 2003).
California tiger salamanders also require dry-season refuge sites in the vicinity of
breeding sites (within 1 mile/1.6 kilometer) (Jennings and Hayes 1994). The
species spends a significant time underground in the burrows of California
ground squirrels, gophers, and other animals, and in soil crevices (Stebbins
2003). Adults emerge from underground to breed, but only for brief periods
during the year. Tiger salamanders breed and lay their eggs primarily in vernal
pools and other ephemeral ponds that fill in winter and often dry out by summer
(Loredo et al. 1996); they sometimes use permanent human-made ponds (e.g.,
stock ponds), reservoirs, and small lakes that do not support predatory fish or
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
2
AMPHIBIANS
California Tiger Salamander (Ambystoma californiense)
bullfrogs (see “Ecological Relationships” discussion below) (Stebbins 1972;
California Wildlife Habitat Relationships 2005; Jennings and Hayes 1994).
The suitability of California tiger salamander habitat is directly proportional to
the abundance of upland refuge sites near aquatic breeding sites. This species
requires underground refugia for cover during the nonbreeding season and during
migration to and from aquatic breeding sites (California Wildlife Habitat
Relationships 2005). Petranka (1998) estimates that 83% of California tiger
salamander utilize rodent burrows for upland refugia. California tiger
salamanders primarily use California ground squirrel burrows as refuge sites, but
they also use logs, piles of lumber, and shrink-swell cracks in the ground for
cover (Holland et al. 1990; Loredo et al. 1996). Botta’s pocket gopher burrows
are also frequently used (Barry and Shaffer 1994; Jennings and Hayes 1994). The
presence and abundance of tiger salamanders in many areas are limited by the
number of small-mammal burrows available; salamanders are typically absent
from areas that appear suitable but lack burrows. Loredo et al. (1996) emphasized
the importance of California ground squirrel burrows as refugia for California
tiger salamanders and suggested that a commensal relationship existed between
the California tiger salamander and California ground squirrel in which tiger
salamanders benefit from the burrowing activities of squirrels. Also, tiger
salamanders apparently do not avoid burrows occupied by ground squirrels
(Loredo et al. 1996).
The proximity of refuge sites to aquatic breeding sites also affects the suitability
of salamander habitat. Adults and juveniles regularly move >0.6 mi (1 km) from
their breeding site, and adults move as far as 1.3 mi (2.2 km) to and from
breeding ponds (California Department of Fish and Game 2010). A recent
trapping effort in Contra Costa County captured California tiger salamanders at
distances ranging from 2,641 feet (805 m) to 3,960 feet (1,207 m) from the
nearest aquatic, breeding site (U.S. Fish and Wildlife Service 2004). Recent
tracking studies indicate that 50–95% of adult CTS disperse to within 492 feet
(150 m) and 2,034 feet (620 m) of their breeding pond, respectively (Trenham
and Shaffer 2005; California Department of Fish and Game 2010). For subadults, 95% are within 2,067 feet (630 m) of the pond, with 85% concentrated
between 656 and 1,969 ft (200–600 m) of it (Trenham and Shaffer 2005;
California Department of Fish and Game 2010).
Loredo et al. (1996) found that tiger salamanders may use the first burrows that
are encountered during movements from breeding to upland sites. In their study
area, where the density of California ground squirrel burrows was high, the
average migration distances between breeding and refuge sites for adults and
juveniles was 118 feet (35.9 m) and 85 feet (26.0 m), respectively. Also, habitat
complexes that include upland refugia relatively close to breeding sites are
considered more suitable because predation risk and physiological stress in
California tiger salamanders probably increases with migration distance.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
3
AMPHIBIANS
California Tiger Salamander (Ambystoma californiense)
Foraging Requirements
Aquatic larvae feed on algae, small crustaceans, and small mosquito larvae for
about 6 weeks after hatching (U.S. Fish and Wildlife Service 2000). Larger
larvae feed on zooplankton, amphipods, mollusks, and smaller tadpoles of Pacific
treefrogs, red-legged frogs, western toads, and spadefoot toads (California
Wildlife Habitat Relationships 2005; U.S. Fish and Wildlife Service 2000).
During estivation, California tiger salamanders eat very little (Shaffer et al. 1993
in U.S. Fish and Wildlife Service 2000). During the fall and winter, adult
salamanders emerge from underground retreats during rain events and on nights
of high relative humidity to feed and migrate to breeding ponds (U.S. Fish and
Wildlife Service 2000). Adults eat earthworms, snails, insects, fish, and small
mammals (Stebbins 1972).
Reproduction
Adult salamanders migrate from upland habitats to aquatic breeding sites during
the first major rainfall events of fall and early winter. During the breeding period,
tiger salamanders lay eggs primarily in vernal pools and other shallow ephemeral
ponds that fill in winter and often dry by summer, as previously mentioned
(Loredo et al. 1996). Spawning usually occurs within a few days after migration,
and adults probably leave the breeding sites at night soon after spawning (Barry
and Shaffer 1994 citing Storer 1925).
Eggs are laid singly or in clumps on both submerged and emergent vegetation
(Stebbins 1972; Shaffer and Fisher 1991; Barry and Shaffer 1994; Jennings and
Hayes 1994). This species will also use permanent human-made ponds (without
predatory fish) for reproduction. In ponds without vegetation, females lay eggs
on objects on the pond bottom or on submerged debris in shallow water
(Jennings and Hayes 1994).
After approximately 2 weeks, the salamander eggs begin to hatch into larvae.
Once larvae reach a minimum body size they metamorphose into terrestrial,
juvenile salamanders. The periods of time salamanders spend in the larval stage
and the size of individuals at the time of metamorphosis seems to be dependent
on many factors. Larvae in small ponds develop faster, while larvae in larger
ponds that retain water for longer periods are larger at time of metamorphosis. At
a minimum, salamanders require ten weeks living in ponded water to complete
metamorphosis, but in general development is completed in 3–6 months
(Petranka 1998). If a pond dries prior to metamorphosis, the larvae will desiccate
and die (U.S. Fish and Wildlife Service 2000). Juveniles disperse from aquatic
breeding sites to upland habitats after metamorphosis (Storer 1925; Holland et al.
1990).
The survival of California tiger salamanders is particularly sensitive to the
duration of ponding in aquatic breeding sites. Suitable breeding sites should
retain water for a minimum of 10 weeks. Because tiger salamanders have a long
developmental period, the longest-lasting seasonal ponds or vernal pools are the
most suitable type of breeding habitat for this species; these pools are also
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
4
AMPHIBIANS
California Tiger Salamander (Ambystoma californiense)
typically largest (Jennings and Hayes 1994). Moreover, large vernal pool
complexes, rather than isolated pools, probably offer the best-quality habitat;
these areas can support a mixture of core breeding sites and nearby refuge habitat
(Shaffer et al. 1993; Jennings and Hayes 1994).
Demography
Local populations of California tiger salamanders may not reproduce during
years of low rainfall when ephemeral pools do not fill (Barry and Shaffer 1994;
Jennings and Hayes 1994). However, it is presumed that the longevity of this
species allows local populations to persist through all but the longest drought
periods (Barry and Shaffer 1994). Individuals have been known to live for more
than 10 years (Trenham et al. 2000 in U.S. Fish and Wildlife Service 2000). In
some populations fewer than 5% of marked juveniles survived to become
breeding adults (Trenham 1998 in U.S. Fish and Wildlife Service 2003). Some
individuals may not breed until six years old, and many individuals breed only
once during a lifetime (U.S. Fish and Wildlife Service 2003). According to
Trenham et al. (2000), the average female breeds 1.4 times and produces 8.5
young that survive to metamorphosis per reproductive effort (69 FR 47215,
August 4, 2004).
Behavior
Adult California tiger salamanders migrate to and congregate at aquatic breeding
sites during warm rains, primarily between November and February (Shaffer and
Fisher 1991; Barry and Shaffer 1994) and are rarely observed except during this
period (Loredo et al. 1996). Dispersal of juveniles from natal ponds to
underground refugia occurs during summer months, when breeding ponds dry
out. Juveniles disperse from breeding sites after spending a few hours or days
near the pond margin (Jennings and Hayes 1994). Dispersal distance varies and
may increase with an increase in precipitation (Trenham 2001).
Ecological Relationships
California tiger salamander larvae and embryos are susceptible to predation by
fish (Stebbins 1972; California Wildlife Habitat Relationships 2005; Shaffer et
al. 1993); thus, tiger salamander larvae are rarely found in aquatic sites that
support predatory fish (Shaffer and Fisher 1991; Shaffer and Stanley 1992;
Shaffer et al. 1993). Aquatic larvae are also susceptible to predation by herons,
egrets, and possibly garter snakes (California Wildlife Habitat Relationships
2005). Shaffer et al. (1993) also found a negative correlation between the
occurrence of California tiger salamanders and the presence of bullfrogs;
however, this relationship was detected only in unvegetated ponds. This suggests
that vegetation structure in aquatic breeding sites may be important for survival.
However, because of their secretive behavior and limited periods above ground,
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
5
AMPHIBIANS
California Tiger Salamander (Ambystoma californiense)
adult California tiger salamanders have few predators (U.S. Fish and Wildlife
Service 2000).
Population Trend
Global:
California State endemic; declining
(California Department of Fish and Game 2010)
State:
Declining (California Department of Fish and Game 2010)
Within HCP Unknown
Study Area:
Threats
In general, California tiger salamander populations have experienced dramatic
declines throughout the historical range of the species, particularly in the Central
Valley, as a result of two primary factors: widespread habitat loss and habitat
fragmentation (California Department of Fish and Game 2010). Both factors are
caused by conversion of valley and foothill grassland and oak woodland habitats
to agriculture and urban development (Stebbins 2003; California Department of
Fish and Game 2010). There is recent evidence of an increase in poor recruitment
years, possibly associated with climate change, in Solano County (California
Department of Fish and Game 2010).
Widespread threats to this species’ survival also include the introduction of
bullfrogs, Louisiana red swamp crayfish, and nonnative fishes (mosquitofish,
bass, and sunfish) into aquatic habitats (59 FR 18353–18354, April 18, 1994,
U.S. Fish and Wildlife Service 2000). Mosquitofish compete with and decrease
the fitness of salamander larvae, resulting in decreased larval survival and size at
metamorphosis (Leyse 2003). Other threats include mortality from vehiclerelated accidents and programs to control burrowing mammals (Barry and
Shaffer 1994; Jennings and Hayes 1994; California Department of Fish and
Game 2010). Burrowing-mammal control programs are considered a threat to
California tiger salamander populations. Rodent control through destruction of
burrows and release of toxic chemicals into burrows can cause direct mortality to
individual salamanders and may result in a decrease of available suitable habitat
(U.S. Fish and Wildlife Service 2000; California Department of Fish and Game
2010).
Overgrazing can threaten populations by degrading wetlands and removing
vegetative cover (Jennings and Hayes 1994). However, appropriate levels of
grazing can have beneficial impacts, promoting large populations of ground
squirrels and providing stock ponds that may be utilized for breeding. Direct
mortality due to vehicle impacts at road crossings may also threaten populations
(U.S. Fish and Wildlife Service 2000).
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
6
AMPHIBIANS
California Tiger Salamander (Ambystoma californiense)
Within the HCP Study Area threats to this species survival and persistence
include conversion of grassland habitat to agricultural uses, destruction of
seasonal wetlands by long-term overgrazing, introduction of exotic predators and
burrowing mammal control programs. Potential impacts from covered activities
under the HCP include road construction, bridge replacement/construction, fence
and gate repair and installation, vegetation management, recreation on lands
owned by the SFPUC, high-traffic grazing areas, and pipeline maintenance.
These activities would affect nonnative grasslands and other upland habitats used
by this species. Construction of roads and bridges would result in permanent
impacts; however, the remaining activities would have only temporary impacts
and would not result in loss of habitat. Grazing activities within aquatic breeding
sites is generally considered positive because it clears vegetation, allowing
greater exposure to sunlight that increases water temperature.
The spread of nonnative plants and increase in nonnative predators can adversely
affect covered California tiger salamanders. Sedimentation, changes in water
quantity and temperature, and road runoff can reduce water quality and pond
holding capacity and affect larval rates of growth and survival. Excessive
suspended sediment can interfere with developing embryos and reduce the
productivity of the food chain and food supplies for California tiger salamander.
In addition, changes in hydrology can favor nonnative predatory species.
Data Characterization
The location database for the California tiger salamander within the HCP study
area includes 24 data records dated from 1961 to 2003 (California Natural
Diversity Database 2008). There are many gaps in data for the California tiger
salamander, notably habitat and population distribution and differentiating
between introduced tiger salamanders and California tiger salamanders (U.S.
Fish and Wildlife Service 2000).
Existing conservation measures for this species include preservation of occupied
habitat, mitigative replacement of lost habitat, and prevention of contamination
of aquatic habitat used by the species. Research has shown that dispersing
juveniles can roam up to one mile from their breeding ponds and that a minimum
of 480 acres of uplands habitat are needed surrounding a breeding pond for longterm survival of the species. Reserves of multiple breeding ponds surrounded by
1,000 acres or more of habitat are recommended to ensure the persistence of the
species (Center for Biological Diversity 2002).
Modeled Species Distribution in HCP Study Area
Figure 2 shows the habitat distribution model for the California tiger salamander
within the 46,700-acre study area.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
7
AMPHIBIANS
California Tiger Salamander (Ambystoma californiense)
Model Description
Model Assumptions
1. All ponds and wetlands (e.g., freshwater marshes and freshwater seeps)
within valley needlegrass grassland, non-native grassland, serpentine
bunchgrass grassland, valley oak woodland, blue oak woodland, oak
savanna, and mixed evergreen forest/oak woodland land-cover types were
considered potential breeding habitat for California tiger salamander.
2. All non-aquatic land cover types, except urban/developed, nursery, and
Diablan sage scrub, within 1 mile of potential breeding sites were considered
potential migration and aestivation habitat for this species.
Rationale
California tiger salamanders inhabit valley and foothill grasslands and the grassy
understory of open woodlands, usually within 1 mile of water (Jennings and
Hayes 1994). The California tiger salamander is terrestrial as an adult and spends
most of its time underground in subterranean refugia. Underground retreats
usually consist of ground-squirrel burrows and occasionally human-made
structures. Adults emerge from underground to breed, but only for brief periods
during the year.
Tiger salamanders breed and lay their eggs primarily in vernal pools and other
ephemeral ponds that fill in winter and often dry out by summer (Loredo et al.
1996); they sometimes use permanent human-made ponds (e.g., stock ponds),
reservoirs, and small lakes that do not support predatory fish or bullfrogs
(Stebbins 1972; California Wildlife Habitat Relationships 2005). Streams are
rarely used for reproduction.
Most populations occur at elevations below 1,500 feet, but tiger salamanders
have been recorded at elevations up to 3,660 feet (1,097 meters) (Stebbins 1972;
Jennings and Hayes 1994; B. Bolster pers. comm.).
Adult salamanders migrate from upland habitats to aquatic breeding sites during
the first major rainfall events of fall and early winter and return to upland habitats
after breeding. This species requires small-mammal (e.g., California ground
squirrel) burrows for cover during the non-breeding season and during migration
to and from aquatic breeding sites (California Wildlife Habitat Relationships
2005). California tiger salamanders also use logs, lumber piles, and shrink-swell
cracks in the ground for cover (Holland et al. 1990) California tiger salamanders
can overwinter in burrows up to 1 mile from their breeding sites (Jennings and
Hayes 1994).
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
8
AMPHIBIANS
California Tiger Salamander (Ambystoma californiense)
Model Results
Within the entire study area there are approximately 56.8 acres of modeled
breeding habitat and 30,505.5 acres of modeled migration and aestivation habitat
for this species.
Results of the habitat distribution model are based on two tiers of analysis. The
first tier of analysis is based on application of the assumptions provided above
using geographic information systems (GIS). Based on this analysis, 3.6 acres of
pond habitat was found to be unsuitable for breeding California tiger salamander.
The remaining ponds in the HCP study area were considered suitable breeding
habitat and subject to the second tier of analysis.
The second tier of analysis involved application of data derived from field
surveys of 68 ponds within the study area. Biologists conducted the pond survey
in September 2003. The purpose of this survey was to provide both physical and
biological data to assess and rank each surveyed pond for breeding habitat
suitability. Of the surveyed ponds, 100% were considered suitable breeding
habitat. Suitable ponds were then ranked as having high suitability (given a score
of 2) or low suitability (given a score of 1) depending on presence of predators.
Based on this characteristic, 37 % of the ponds were considered highly suitable
breeding habitat while 63% of the ponds were considered moderately suitable
breeding habitat (Figure 2).
The final step in the second tier of analysis was to extrapolate the findings from
the pond survey (68 pond sample) to all ponds in the study area considered
suitable after the first tier of analysis. The goal of the extrapolation is to
determine the acres of suitable pond breeding habitat in the study area based on
the results of our pond survey. For the California tiger salamander, our analysis
indicates that 100% of the surveyed ponds contain suitable breeding habitat.
(For the extrapolation, all ponds receiving a score of 1 or 2 were considered
suitable breeding habitat.) The result of this analysis is a total of 56.8 acres of
modeled breeding habitat comprised of 36 acres of pond habitat and 20.8 acres of
wetland habitat.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
9
HCP Study Area
Breeding Range
0
100
MILES
FIGURE 1
California Tiger Salamander (Ambystoma californiense)
Distribution
Source: Adapted USFWS 2003.
Figure 2 Habitat Distribution Model for California Tiger Salamander (Ambystoma californiese)
Legend
d
te
ou
!
(
a
er
!
(
!
(
u
!
( !
(
!
(
!
(
on
Reservoir
Secondary Road
Study Area
County Line
SFPUC Ownership
!
(
k
!
(
!
(!
(
(!
!
(
Primary Road
!
(
ee
Cr
e !(
rs
h
Stream
!
(
!
(
n
dia
In
ad
Cre e k
lc
Ro
lch
!
(
!
(
p
Known Occurrence
(Denotes one occurrence
within polygon)
G
ida n
We
s
ne
Hay h
Gulc
!
(
!
(
!
(
!
( !
(
A!(!(!(
p
!
(
!
(
!
(!
!
( (
k
re e
aC
She r
!
(
s
!
(
!
(
!
(
!
(
Potential Migration and Aestivation Habitat
m
!
(
!
(
!
(
ia
!
(
!
(
!
(
!
(!
(
!
(
!
(
(
!!
(
ill
!
(
!
(
!
(
!
(
!
(
!
(
!
(
W
Unsurveyed pond
Suitable Breeding Habitat
!
(
ek
!
(
!
(
!
(
!
(
!
(
!
(
!
(
!
(
!
(
C
re
!
(
!
( (
!
!
(
Va
lle
!
(
!
(
!
(
!
(
!
(
!
(
!
(
(
!!
(
!
(
!
(!
(
n A
!
(
st
Co
La
!
(
Sa
!
(
!
(
y
!
(
Fremont
Pond Habitat Suitability = Not Suitable
(Note: Core Breeding Habitat in
ponds cannot be seen at
this scale, and are overwritten
by Pond Habitat Suitablity points.)
De
l
!
(
!
(
(
!
( !
ni
!
(
lle
!
(
Sa n
!
(
d
s Roa
!
(
to
An
!
(
o
ni
!
(
ra
Calave
80
ir
vo
nt o
!
(
Va
I
!
(
!
(
nol
-6
( !
!
(!
(
!
(
!
(
!
(
k
Su
!
(
ree
!
(
!
(
!
(
Pond Habitat Suitability = Moderate
!
(
!
(
e ek
!
(
!
(!
(
!
(!
(!
(
!
(
(
!!
(
Pond Habitat Suitability = High
!
(
Unsurveyed Ponds
!
(
Vallec ito '
sC
ed
!
( !
(
!
(
!
(
!
(
Cr
!
(
s R
Re
s
m
!
(
(!
(
!
(!
!
(
ecito
o
Al a
Fo o
Ni
le
s
Sunol
d
R
V all
d
oa
/ R
ke
La
oa
ill
a
de la L a gun
R
th
84
80
o
roy
C anyon
Surveyed Ponds
I-6
Ar
R
!
(
id
g
L
n
de
ey
Cr
ee
e
!
(
!
(
k
!
(
(!
!
(
!
(
!
(
A lame
d a Cr
ee
k
©
(
!!
(
!
(
!
(
Oa
!
(
!
(
Ca
la
0
I - 68
We
ller
0
I-88
ve
Re
Ro ad
!
(
se
rvo
ir
0
o
rt
!
(
d
oa
!
(
!
(
!
(
Ho
e
nd
y
!
(
o
!
(
R
!
(
id
!
(
g
as
e
er
Cala v
e
Cre
!
(
!
(
!
(
!
(
!
(
k
Mt.
Day
!
(
!
(
2
Miles
o
v
1
1:100,000
!
(
P
0.5
Santa Clara Co.
!
(
!
(
Ma r s
!
(
Alameda Co.
!
(
!
(
!
(
h R
d g !(
e
!
(
ro y
Ar
as R o a d
er
Felt
!
(
!
(
!
(
Ca la v er
Milpitas
Ri
ra s
!
(
d
Roa
k
AMPHIBIANS
Foothill Yellow-Legged Frog (Rana boylii)
Foothill Yellow-Legged Frog (Rana boylii)
Status
State:
Species of Special Concern
Federal:
None
Critical Habitat:
N/A
Range
Historically, foothill yellow-legged frog (Rana boylii) occurred from west of the
crest of the Cascade Mountains in Oregon south to the Transverse Ranges in Los
Angeles County, and in the Sierra Nevada foothills south to Kern County
(Zweifel 1955; Stebbins 2003). An isolated population was reported in Sierra San
Pedro Martir, Baja Mexico (Loomis 1965). The current range excludes coastal
areas south of northern San Luis Obispo County and foothill areas south of
Fresno County where the species is apparently extirpated (Jennings and Hayes
1994) (Figure 1). Its known elevation range extends from near sea level to
approximately 2,040 meters (6,692 feet) above sea level (Stebbins 2003).
Occurrences within the HCP Study Area
According to the California Natural Diversity Database (CNDDB) (2008) there
are 5 documented occurrence records of foothill yellow-legged frog in Alameda
County and 5 occurrence records in the Habitat Conservation Plan (HCP) study
area (4 in Alameda Creek and 1 in Arroyo Hondo). All of these CNDDB
occurrence records are considered extant and were recorded within the last 20
years. Surveys for foothill yellow-legged frog have been conducted in the HCP
study area. During these surveys frogs have been observed in Arroyo Hondo and
Alameda Creek from the confluence of Calaveras Creek to upstream of the
diversion tunnel. The most recent survey was conducted by East Bay Regional
Park on parkland. Foothill yellow-legged frogs were documented in multiple
reaches of Alameda Creek in areas adjacent to the HCP study area (Bobzien and
DiDonato 2007).
Biology
Habitat
Foothill yellow-legged frogs require shallow, flowing water in small to
moderate-sized streams with at least some cobble-sized substrate (Hayes and
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
1
AMPHIBIANS
Foothill Yellow-Legged Frog (Rana boylii)
Jennings 1988; Jennings 1988). This habitat is believed to favor oviposition
(Storer 1925; Fitch 1936; Zweifel 1955) and refuge habitat for larvae and
postmetamorphs (Hayes and Jennings 1988; Jennings 1988). This species has
been found in streams without cobble (Fitch 1938; Zweifel 1955), but it is not
clear whether these habitats are regularly used (Hayes and Jennings 1988;
Jennings and Hayes 1994). Foothill yellow-legged frogs are usually absent from
habitats where introduced aquatic predators, such as various fishes and bullfrogs,
are present (Hayes and Jennings 1986, 1988; Kupferberg 1994). The species
deposits its egg masses on the downstream side of cobbles and boulders over
which a relatively thin, gentle flow of water exists (Storer 1925; Fitch 1936;
Zweifel 1955). The timing of oviposition typically follows the period of high
flow discharge from winter rainfall and snowmelt (Jennings and Hayes 1994).
The embryos have a critical thermal maximum temperature of 26ºC
(Zweifel 1955).
Breeding Habitat Requirements
Foothill yellow-legged frogs in California generally breed between March and
early June (Storer 1925; Grinnell et al. 1930; Wright and Wright 1949; Jennings
and Hayes 1994). Masses of eggs are deposited on the downstream side of
cobbles and boulders. After oviposition, a minimum of approximately 15 weeks
is required to reach metamorphosis, which typically occurs between July and
September (Storer 1925; Jennings 1988). Larvae attain adult size in 2 years
(Storer 1925).
Foraging Requirements
Adult foothill yellow-legged frogs feed primarily on both aquatic and terrestrial
insects (Fitch 1936); tadpoles preferentially graze on algae (Jennings and
Hayes 1994). Postmetamorphs eat aquatic and terrestrial insects (Storer 1925;
Fitch 1936).
Demography
Masses of 300 to 1,200 eggs are deposited during oviposition by each breeding
female. Juvenile and adult survivorship is unknown. Adult longevity is unknown.
Dispersal
There is no information about migration from breeding areas or seasonal
movements for this species; however, foothill yellow legged frogs are rarely seen
far from perennial water.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
2
AMPHIBIANS
Foothill Yellow-Legged Frog (Rana boylii)
Behavior
This species is primarily diurnal and in warmer climates it is active year-round.
Adults bask on rocks but will quickly dive into the water and hide under a rock if
threatened.
Ecological Relationships
Garter snakes are considered one of the most prominent predators of foothill
yellow-legged frog tadpoles (Fitch 1941; Zweifel 1955; Lind 1990; Jennings and
Hayes 1994). Salamanders, including the rough-skinned newt (Taricha torosa),
are believed to prey on the species’ eggs.
Data Characterization
The location database for the foothill yellow-legged frog within its known range
in California includes 464 occurrence records dated from 1958 to 2007. Of these
all but one occurrence are presumed extant. A moderate amount of literature is
available for the foothill yellow-legged frog because of its local availability for
study and the recent trend in global decline in amphibians. Most of the literature
pertains to habitat requirements, population trends, ecological relationships,
threats, and conservation efforts.
Population Trend
Global:
Unknown, but probably declining
State:
Unknown, but probably declining
Within HCP Unknown
Study Area:
Threats
Habitat loss and degradation, introduction of exotic predators, and toxic
chemicals (including pesticides) pose continued and increasing threats to the
long-term viability amphibians throughout California (Jennings and Hayes 1994).
The primary covered activities with the potential to impact foothill yellow-legged
frog are controlled releases (e.g., valve releases) and releases for fishery
enhancement. Specifically, any covered activity that disrupts normal stream
flows including timing of flows, water depths, velocities, water temperature, or
disturbs channel substrate can affect foothill yellow-legged frogs (Lind 2005).
Direct and indirect impacts associated with changed instream flows include:
desiccation or stranding of eggs or tadpoles due to rapid reductions in flow;
delays in breeding and embryo or tadpole development due to temperature;
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
3
AMPHIBIANS
Foothill Yellow-Legged Frog (Rana boylii)
declines in spring and summer algal productivity; reduced resources for tadpoles;
reduced insect abundance and food-web repercussions. (Lind 2005; Kupferberg
et al. 2009.) If sufficiently high, instream releases to benefit salmonids during the
spring of otherwise dry years could dislodge egg masses and displace larvae
downstream.
Overgrazing resulting in damage to riparian vegetation can threaten foothill
yellow legged frog populations by raising stream temperatures and reducing
cover. Additionally, within the Alameda Creek Watershed, certain O&M
activities that affect riparian and other streamside habitat (e.g., bridge
replacement and construction) could result in impacts to this species.
Modeled Species Distribution
Figure 2 shows the habitat distribution model for the foothill yellow-legged frog
within the 46,700-acre study area.
Model Description
Model Assumptions
1. Core Habitat: Perennial streams in central coast live oak riparian forest, coast
live oak riparian forest, sycamore alluvial woodland, willow riparian
forest/scrub, white alder riparian forest, mixed evergreen forest/oak
woodland, valley oak woodland, blue oak woodland, oak savanna, valley
needlegrass grassland, non-native grassland, serpentine bunchgrass
grassland, and Diablan sage scrub land-cover types.
2. Low-use habitat: Other streams in the same land cover types listed above.
Rationale
Foothill yellow-legged frogs are stream-dwelling amphibians that require
shallow, flowing water in small to moderate-sized perennial streams with at least
some cobble-sized substrate (Hayes and Jennings 1988; Jennings 1988). This
species has also been found in perennial streams without cobble (Fitch 1938;
Zweifel 1955), but it is not clear whether these habitats are regularly used (Hayes
and Jennings 1988; Jennings and Hayes 1994). Regardless, the presence of
cobble substrate, and specifically the size of cobble, has not been mapped for
streams in the study area. So this level of microhabitat detail could not be
included as a model parameter. Most of this species’ life is spent in or near water.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
4
AMPHIBIANS
Foothill Yellow-Legged Frog (Rana boylii)
Model Results
[Note to Reader: Acres of impacts will be translated to linear miles of impact for
Public Draft]
Within the entire study area there are 285.9 acres of modeled core habitat and
644 acres of low-use habitat for this species. The habitat distribution model is
based on the assumptions provided above. Core habitat primarily occurs in
Alameda Creek near Sunol and north of Calaveras Reservoir. Areas of core
habitat also occur in La Costa Creek, Indian Creek, Arroyo Hondo and a few
unnamed perennial drainages. Since stream substrate could not be included as a
model parameter, due to lack of that type of information, these model results
overestimate the presence of suitable habitat in the study area. All documented
occurrence locations fit within the boundaries of the model.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
5
Species Range
HCP Study Area
Breeding Range
0
100
MILES
FIGURE 1
Foothill Yellow-Legged Frog (Rana boylii)
Distribution
Source: Adapted from Zeiner et al. 1984.
Figure 2 Habitat Distribution Model for Foothill Yellow-Legged Frog (Rana boylii)
Legend
Ni
le
R
oa
Sunol
d
R
i ll
th
ou
te
84
s
ecito
V all
Ro
ad
/ R
Core Habitat
Low-use Habitat
Vallecito
's C
A la
m
ree
ke
La
s
Canyon
Fo o
d
ro
80
I-6
e la L a g una
yo d
Ar
k
ed
e ek
De
l
n A
Re
Cr
ee
ni
o
Sa n
to
An
W
k
ill
ia
m
s
G
Stream
u
lc
Primary Road
Reservoir
Secondary Road
Study Area
h
La
st
Co
County Line
p
k
o
ee
rs
Cr
e
n
Cr e e k
p
dia
In
ad
s
SFPUC Ownership
k
Ro
yne
Ha
h
Gulc
lch
re e
id an
aC
Sher
A
We
Fremont
Known Occurence
Va
lle
io
I
Sa
on
d
s Roa
alavera
C
y
lle
Va
nol
80
-6
ir
vo
nt
Su
se
r
a
Cr
n
R
id
©
g
e
L
de
ey
n
ee
Cr
k
A lam e
d a Cr
ee
k
Oa
la
Ca
I - 68
We
0
lle r
0
I-88
ve
Ro ad
Re
se
rvo
e
0
Santa Clara Co.
ir
o
rt
Ho
ve
o
roy
Ar
P
y
h R
d
oa
Ma r s
Alameda Co.
dg
0.5
1
1:100,000
ras R oa d
r
F elte
Ri
ra s
Cal a ve
Milpitas
d
Ro a
k
nd
o
R
id
g
Calav
e
er
as
e
Cr e
k
Mt.
Day
2
Miles
BIRDS
Tricolored Blackbird (Agelaius tricolor)
Tricolored Blackbird (Agelaius tricolor)
Status
State:
Bird Species of Special Concern, First Priority
(California Department of Fish and Game 2008)
Federal:
Migratory Bird Treaty Act (16 USC 703-712)
Critical Habitat:
N/A
Range
Tricolored blackbirds (Agelaius tricolor) are largely endemic to California, and
more than 99% of the global population occurs in the state. In any given year,
more than 75% of the breeding population can be found in the Central Valley
(Hamilton 2000). Small breeding populations also exist at scattered sites in
Oregon, Washington, Nevada, and western coastal Baja California (Beedy and
Hamilton 1999).
The species’ historical breeding range in California included the Sacramento and
San Joaquin Valleys, lowlands of the Sierra Nevada south to Kern County, the
coast region from Sonoma County to the Mexican border, and sporadically on the
Modoc Plateau (Dawson 1923; Neff 1937; Grinnell and Miller 1944).
Population surveys and banding studies of tricolored blackbirds in the Central
Valley from 1969 through 1972 concluded that their geographic range and major
breeding areas were unchanged since the mid-1930s (DeHaven et al. 1975a).
Since 1980, active breeding colonies have been observed in 46 California
counties, including Alameda County. In recent decades, breeding colonies have
been observed in all Central Valley counties and east into the foothills of the
Sierra Nevada (Beedy and Hamilton 1997, 1999; Hamilton 2000). The species
also breeds locally along the California coast from Humboldt to San Diego
Counties; on the Modoc Plateau and western edge of the Great Basin (mostly
Klamath Basin); in lowlands surrounding the Central Valley; and in western
portions of San Bernardino, Riverside, and San Diego Counties. The species also
breeds in marshes of the Klamath Basin in Siskiyou and Modoc Counties, and
Honey Lake Basin in Lassen County (Figure 1). During winter, virtually the
entire population of the species withdraws from Washington, Oregon (although a
few remain), Nevada, and Baja California, and wintering populations shift
extensively within their breeding range in California (Beedy and Hamilton 1999).
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
1
BIRDS
Tricolored Blackbird (Agelaius tricolor)
Occurrences within the HCP Study Area
Breeding colonies of tricolored blackbird have been documented in the Sunol
Valley three times since 1971. Approximately 1,200 individuals were
documented nesting near Alameda Creek and Highway 680 in 1971, and
approximately 2,000 individuals were documented at the eastern end of San
Antonio Reservoir, along with about 150 more in Sunol Valley and a small
colony of about 200 birds along Ranch Road, all in 1994 (California Natural
Diversity Database 2008; H. Peeters pers. comm.) In 2009, approximately 1,000
individuals were observed nesting in tule and cattails in coves along the northern
edge of San Antonio Reservoir; the main colony was in the north-eastern most
cove, visible from Ranch Road (H. Peeters pers. comm.). In addition, tricolored
blackbirds have been seen at a pond north of the west end of the San Antonio
Reservoir, although nesting has not been documented there. The species has,
however, been observed nesting in the quarry areas west of Calaveras Road in
many years since 1970 (H. Peeters pers. comm.). Most recently, in early summer
2010, flocks of several hundred tricolored blackbirds were observed feeding in
annual grasslands within the Sycamore woodlands along Alameda Creek
(Dettman and Weinberg 2010 SFPUC monitoring surveys for Alameda Siphon
No. 4 Project). Tricolored blackbirds are considered “itinerant breeders” (i.e.,
nomadic breeders) where individuals/colonies can breed in different
locations/regions among years, so while tricolored blackbirds may use the HCP
area for breeding or forage on a fairly regular basis, the specific pattern of use is
expected to be highly variable from year to year.
Biology
Habitat
Tricolored blackbirds have three basic requirements for selecting their breeding
colony sites: open, accessible water (in some cases, a very modest creek
suffices); a protected nesting substrate, including either flooded, thorny, or spiny
vegetation; and a suitable foraging space providing adequate insect prey within a
few miles of the nesting colony (Hamilton et al. 1995; Beedy and Hamilton 1997,
1999). Almost 93% of the 252 breeding colonies reported by Neff (1937) were in
freshwater marshes dominated by cattails and tule (Typha spp. and
Schoenoplectus spp.). The remaining colonies in Neff's study were in willows
(Salix spp.), blackberries (Rubus spp.), thistles (Cirsium and Centaurea spp.), or
nettles (Urtica sp.). In contrast, only 53% of the colonies reported during the
1970s were in cattails and bulrushes (DeHaven et al. 1975a).
An increasing percentage of tricolored blackbird colonies in the 1980s and 1990s
were reported in Himalayan blackberries (Rubus discolor) (Cook 1996), and
some of the largest recent colonies have been in silage and grain fields (Hamilton
et al. 1995; Beedy and Hamilton 1997; Hamilton 2000). Other substrates where
tricolored blackbirds have been observed nesting include giant cane (Arundo
donax), safflower (Carthamus tinctorius) (DeHaven et al. 1975a), tamarisk trees
(Tamarix spp.), elderberry/poison oak (Sambucus spp. and Toxicodendron
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
2
BIRDS
Tricolored Blackbird (Agelaius tricolor)
diversilobum), and riparian scrublands and woodlands (e.g., Salix, Populus,
Fraxinus) (Beedy and Hamilton 1999). In 2009 in Sunol Valley, some of the
birds nested in mustard (Brassica sp.) and in coyote and mulefat bushes
(Baccharis pilularis and B. salicifolia).
Foraging habitats in all seasons include annual grasslands; wet and dry vernal
pools and other seasonal wetlands, agricultural fields, cattle feedlots, and dairies.
Tricolored blackbirds also forage occasionally in riparian scrub habitats and
along marsh borders. High-quality foraging areas include irrigated pastures,
lightly grazed rangelands, dry seasonal pools, mowed alfalfa fields, feedlots, and
dairies (Beedy and Hamilton 1999).
Foraging Requirements
Foods delivered to tricolored blackbird nestlings include beetles and weevils,
grasshoppers, caddisfly larvae, moth and butterfly larvae, and dragonfly larvae
(Orians 1961a; Crase and DeHaven 1977; Skorupa et al. 1980; Beedy and
Hamilton 1999). Breeding-season foraging studies in Merced County showed
that animal matter makes up about 91% of the food volume of nestlings and
fledglings, 56% of the food volume of adult females, and 28% of the food
volume of adult males (Skorupa et al. 1980).
Adults may continue to consume plant foods throughout the nesting cycle, but
they also forage on insects and other animal foods. Immediately before and
during nesting, adult tricolored blackbirds are often attracted to the vicinity of
dairies, where they take high-energy items from livestock feed rations. Adults
with access to livestock feed (such as cracked corn) begin providing it to
nestlings when they are about 10 days old (Hamilton et al. 1995). More than 88%
of all winter food in the Sacramento Valley is plant material, primarily seeds of
rice and other grains, but also weed seeds (Crase and DeHaven 1978). In winter,
tricolored blackbirds often associate with other blackbirds, but flocks as large as
15,000 individuals (almost all tricolored blackbirds) may congregate at one
location and disperse to foraging sites (Beedy and Hamilton 1999).
Reproduction
Tricolored blackbirds are closely related to red-winged blackbirds (Agelaius
phoeniceus), but the two species differ substantially in their breeding ecology.
Red-winged blackbird pairs defend individual territories, while tricolored
blackbirds are among the most colonial of North American passerine birds (Bent
1958; Orians 1961a, 1961b, 1980; Orians and Collier 1963; Payne 1969; Beedy
and Hamilton 1999). As many as 20,000 or 30,000 tricolored blackbird nests
have been recorded in cattail marshes of 4 hectares (9 acres) or less (Neff 1937;
DeHaven et al. 1975a), and individual nests may be built less than 0.5 meter (1.5
feet) apart (Neff 1937). Tricolored blackbirds’ colonial breeding system may
have adapted to exploit a rapidly changing environment where the locations of
secure nesting habitat and rich insect food supplies were ephemeral and likely to
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
3
BIRDS
Tricolored Blackbird (Agelaius tricolor)
change each year (Orians 1961a; Orians and Collier 1963; Collier 1968; Payne
1969).
Tricolored blackbird nests are bound to upright plant stems from a few
centimeters to about 1.8 meters (6 feet) above water or ground (Baicich and
Harrison 1997); however, nests in the canopies of willows and ashes may be
more than 3.7 meters (12 feet) high (Hamilton pers. comm.). Their nests are
rarely built on the ground (Neff 1937), although they have been observed to do
so in drained cattail marshes such as are found near gravel pits (H. Peeters pers.
comm.). Deep cup nests are constructed with outer layers of long leaves (e.g.,
cattail thatch, annual grasses, or forbs) woven tightly around supporting stems.
The inner layers are coiled stems of grasses lined with soft plant down, mud, or
algal fibers. Nest building takes about four days (Payne 1969).
Egg laying can begin as early as the second day after nest initiation but ordinarily
starts about four days after the local arrival of tricolored blackbirds at breeding
sites (Payne 1969). One egg is laid per day, and clutch size is typically three to
four eggs (Payne 1969; Hamilton et al. 1995). Emlen (1941) and Orians (1961b)
estimated the incubation period at 11 or 12 days, while Payne (1969) estimated it
to be 11–14 days. About nine days generally elapse from hatching until the oldest
nestling is willing to jump from the nest when disturbed. Young require about 15
days from this prefledging date until they are independent of their parents. Thus,
one successful nesting effort for a reproductive pair takes about 45 days
(Hamilton et al. 1995). Synchronized second broods within a colony may be
initiated as little as 30 days after the first brood. Individual pairs may nest two or
more times per year.
Demography
Banding studies, summarized by Neff (1942) and DeHaven and Neff (1973),
indicated that tricolored blackbirds can live for at least 13 years, but most live for
much shorter periods. There are no annual survivorship studies of tricolored
blackbird, and available banding data are inadequate to provide this information
(Beedy and Hamilton 1999).
Behavior
During the breeding season, tricolored blackbirds exhibit itinerant breeding,
commonly moving to different breeding sites each season (Hamilton 1998). In
the north Central Valley and northeastern California, individuals move after first
nesting attempts, both successful and unsuccessful (Beedy and Hamilton 1997).
Banding studies indicate that significant movement into the Sacramento Valley
occurs during the postbreeding period (DeHaven et al. 1975b).
In winter, numbers of tricolored blackbirds decrease in the Sacramento Valley
and increase in the Sacramento–San Joaquin River Delta and north San Joaquin
Valley (Neff 1937; Orians 1961a; Payne 1969; DeHaven et al. 1975b). By late
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
4
BIRDS
Tricolored Blackbird (Agelaius tricolor)
October, large flocks also congregate in pasturelands in southern Solano County
and near dairies on Point Reyes Peninsula in Marin County (Beedy and Hamilton
1999). Other birds winter in the central and southern San Joaquin Valley.
Concentrations of more than 15,000 wintering tricolored blackbirds may gather
at one location and disperse up to 32 kilometers (20 miles) to forage (Neff 1937;
Beedy and Hamilton 1999). Individual birds may leave winter roost sites after
less than three weeks and move to other locations (Collier 1968), suggesting
winter turnover and mobility. In early March/April, most birds vacate the
wintering areas in the Central Valley and along the coast and move to breeding
locations in the Sacramento and San Joaquin Valleys (DeHaven et al. 1975b).
Tricolored blackbirds are highly colonial and sometimes polygynous, with one to
four females pairing with one male (Payne 1969). Historic colonies of over
200,000 pairs have been documented, occupying 24 hectares of cattail marsh
(Neff 1937). This social cohesion is retained during the nonbreeding season as
birds form large foraging and roosting flocks. These flocks may consist solely of
tricolors, or they may be mixed flocks with red-winged blackbirds, Brewer’s
blackbirds, brown-headed cowbirds, and European starlings (Beedy and
Hamilton 1999).
Males defend only the immediate areas around the nests. Male territory size
ranges from 1.8 square meters (m2) (19.38 square feet) (Lack and Emlen 1939) to
3.25 m2 (35 square feet) (Orians 1961b). Average size of recently established
territories of six banded males at two different colonies was 3.25 m2 (35 square
feet); volumetric territories in willows were calculated to be 8.5–11.3 cubic
meters (300–400 cubic feet) (Collier 1968). Some Himalayan blackberry colonies
have nesting densities up to six nests/m2 (0.56 nest/square foot) (Cook and
Hamilton pers. comms.). After one week of nest-building and egg-laying, males
may cease territorial defense (Orians 1961b).
Most tricolored blackbirds forage within 5 kilometers (3.1 miles) of their colony
sites (Orians 1961a), but commute distances of up to 15 kilometers (9.3 miles)
have been reported (Beedy and Hamilton 1999). Short-distance foraging (i.e.,
within sight of the colony) for nestling provisioning also is common. Both sexes
are known to provision the nestlings (Beedy and Hamilton 1999).
Proximity to suitable foraging habitat appears to be extremely important for the
establishment of colony sites, as tricolored blackbirds always forage, at least
initially, in the field containing the colony site (Cook 1996). However, usually
only a minor fraction of the area within the commuting range of a colony
provides suitable foraging habitat. For example, within a 5-kilometer (3-mile)
radius there may be low-quality foraging habitats such as cultivated row crops,
orchards, vineyards, and heavily grazed rangelands in association with highquality foraging areas such as irrigated pastures, lightly grazed rangelands, vernal
pools, and recently mowed alfalfa fields (Beedy and Hamilton 1999; Cook 1999).
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
5
BIRDS
Tricolored Blackbird (Agelaius tricolor)
Ecological Relationships
Tricolored blackbirds occupy a unique niche in the Central Valley/coastal
marshland ecosystems. In areas where the number of tricolored blackbirds is
high, they are both aggressively and passively dominant to—and often
displace—sympatric marsh nesting species, including red-winged and yellowheaded blackbirds (Orians and Collier 1963; Payne 1969).
Population Trend
Global:
Declining
State:
Declining (Beedy and Hamilton 1997, 1999)
Within HCP Unknown
Study Area:
The first systematic surveys of tricolored blackbirds’ population status and
distribution were conducted by Neff (1937, 1942). During a five-year period, he
found 252 breeding colonies in 26 California counties; the largest colonies were
in rice-growing areas of the Central Valley. He observed as many as 736,500
adults per year (1934) in just eight Central Valley counties. The largest colony he
observed was in Glenn County; it contained more than 200,000 nests (about
300,000 adults) and covered almost 24 hectares (60 acres). Several other colonies
in Sacramento and Butte Counties contained more than 100,000 nests (about
150,000 adults).
DeHaven et al. (1975a) estimated that the overall population size in the
Sacramento and northern San Joaquin valleys had declined by more than 50%
since the mid-1930s. They performed intensive surveys and banding studies in
the areas surveyed by Neff (1937) and observed significant declines in tricolored
blackbird numbers and the extent of suitable habitat in the period since Neff’s
surveys. Orians (1961a) and Payne (1969) observed colonies of up to 100,000
nests in Colusa, Yolo, and Yuba Counties, but did not attempt to survey the
entire range of the species.
The U.S. Fish and Wildlife Service, the California Department of Fish and Game,
and California Audubon cosponsored intensive tricolored blackbird surveys
carried out by volunteers in suitable habitats throughout California in 1994, 1997,
1999, and 2000 (Hamilton et al. 1995; Beedy and Hamilton 1997; Hamilton
2000). Local, regional, and statewide tricolored blackbird populations have
experienced major declines since 1994. Statewide totals of adults in four lateApril surveys covering all recently known colony sites were 369,359 (1994);
237,928 (1997); 104,786 (1999); and 162,508 (2000). Even though results from
the 2008 statewide survey indicate that the total number of adults is
approximately 395,321 and could suggest a stabile or increase in population there
are no known active breeding colonies inside of the study area. Of the previously
documented colonies in Alameda County only one was occupied during the 2008
nesting season. The twenty-seven birds located at the Ames and Dalton Colony is
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
6
BIRDS
Tricolored Blackbird (Agelaius tricolor)
a colony in north Livermore and is outside of the study area. The other colonies
that are within the study area were not occupied during the 2008 breeding survey.
Although there was one bird seen along Sheridan Road during the survey,
breeding was not confirmed (<http://tricolor.ice.ucdavis.edu/node/628>).
These surveys also identified several important distribution and population trends
for tricolored blackbirds:

Local, regional, and statewide populations and distributions vary from year
to year.

Sixty percent of all tricolored blackbirds located in all years were found in
the 10 largest colonies.

Seventy percent of all tricolored blackbird nests and 86% of all foraging by
nesting birds were on private agricultural lands.

In some portions of their range, tricolored blackbirds have declined or have
been eliminated; the species has been subject to local extirpation in most of
Yolo County and portions of southern Sacramento County.
Threats
The greatest threats to this species are the direct loss and alteration of habitat, but
other human activities and predation also threaten tricolored blackbird
populations (Beedy and Hamilton 1999).
Habitat Loss and Alteration
Most native habitats that once supported nesting and foraging tricolored
blackbirds in the Central Valley have been altered by urbanization and unsuitable
agricultural uses, including vineyards, orchards, and row crops (Frayer et al.
1989; Wilen and Frayer 1990). In Sacramento County, a historic breeding center
of the species, the conversion of grassland and pastures to vineyards expanded
from 3,050 hectares (7,536 acres) in 1996 to 5,330 hectares (13,171 acres) in
1998 (DeHaven 2000). Many former agricultural areas within the historical range
of tricolored blackbird are now being urbanized; in western Placer County, where
tricolored blackbirds forage in the ungrazed annual grasslands associated with
rural subdivisions, suitable habitat will be largely eliminated as current land
conversion patterns continue.
In some places, historical tricolored blackbird breeding and foraging habitats
have been eliminated and there is currently little or no breeding effort where
there once were large colonies (Orians 1961a; Beedy et al. 1991). Elsewhere,
tricolored blackbirds have shifted from cattails as a primary nesting substrate
(Neff 1937) to Himalayan blackberries (DeHaven et al. 1975a), and more
recently to cereal crops and barley silage (Hamilton et al. 1995).
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
7
BIRDS
Tricolored Blackbird (Agelaius tricolor)
Other Human Activities
Nests and nest contents in cereal crops and silage are often destroyed by
agricultural operations (Hamilton et al. 1995; Beedy and Hamilton 1997). Other
factors that may affect the nesting success of colonies in agricultural areas
include herbicide and pesticide applications and spraying for mosquito abatement
(Beedy and Hamilton 1999).
Predation
Predation is at present (i.e., 1985–2002) a major cause of complete nesting
failure at some tricolored blackbird colonies in the Central Valley. Historical
accounts documented the destruction of nesting colonies by a diversity of avian,
mammalian, and reptilian predators. Recently, especially in permanent
freshwater marshes of the Central Valley, entire colonies (>50,000 nests) have
been lost to black-crowned night-herons, common ravens, coyotes, and other
predators (Beedy and Hayworth 1992; Beedy and Hamilton 1999).
Threats in the HCP Area
Reservoir operations during the breeding period can destroy entire colonies if
they are located in a reservoir. Increasing reservoir levels can flood nests, killing
any eggs or young in the nests. Decreasing reservoir levels can leave eggs or
young exposed to terrestrial predators such as coyote or raccoons. Pipeline
maintenance occurring in or near wetlands would temporarily affect these areas
and could result in short-term impact on this species. Direct impacts on tricolored
blackbird foraging habitat could occur within grassland due to vegetation
management and grazing activities as well as from recreational activities.
Indirect impacts on tricolored blackbird include increased noise, and vehicle
traffic from covered operations and maintenance (O&M) activities and possibly
from some HCP implementation activities. Some roads and bridges may be
constructed, and this could increase edge effects associated with roads.
Data Characterization
Statewide surveys were conducted for tricolored blackbirds in California in 1994,
1997, 1999, 2000, and 2008 (Hamilton et al. 1995; Beedy and Hamilton 1997;
Hamilton 2000; R. Kelsey pers. comm.). Additional surveys include data on local
distribution and population trends (Neff 1937; DeHaven et al. 1975a). Because
this species is nomadic with erratic movement behavior, local occurrence data
provide only limited information on long-term small area use patterns. This
species forages and breeds in specific locations of the study area with freshwater
marshes dominated by cattails of bulrushes, or in areas with suitable willow,
mule fat, blackberry, thistle, or nettle habitat.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
8
BIRDS
Tricolored Blackbird (Agelaius tricolor)
A moderate amount of literature is available for the tricolored blackbird because
it is a highly visible colonial bird species commonly associated with wetland
habitat. Beedy and Hamilton (1999) provide a comprehensive review of
information available on general natural history, behavior, distribution and
population changes, known demographics and population regulation, and
conservation and management. No range-wide management plan has been
developed.
Modeled Species Distribution in HCP Study Area
Figure 2 shows the habitat distribution model for the tricolored blackbird within
the 46,700-acre study area.
Model Description
Model Assumptions
1. Core Breeding Habitat: freshwater marshes and ponds adjacent to grassland
or other high quality foraging habitat.
2. Primary Foraging Habitat: cultivated agriculture, valley needlegrass
grassland, non-native grassland, serpentine bunchgrass grassland, and
freshwater seep land-cover types.
Rationale
Tricolored blackbirds are typically associated with emergent freshwater marshes
dominated by cattails or bulrushes, with some colonies occurring in willows,
blackberries, thistles, and nettles associated with sloughs and natural channels
(Neff 1937). Recently, colonies have been observed in a diversity of upland and
agricultural areas (Collier 1968; Cook 1996), riparian scrublands and woodlands
(Orians 1961a; DeHaven et al 1975a; Beedy et al. 1991; Hamilton et al. 1995;
Beedy and Hamilton 1999).
Small breeding colonies have been documented at public and private lakes,
reservoirs, and parks surrounded by shopping centers, subdivisions, and other
urban development. Adults from these colonies generally forage in nearby
undeveloped upland areas. Beedy and Hamilton (1999) predict that these small,
urban wetlands and upland foraging habitats may continue to accommodate
tricolored blackbirds in the future unless they are eliminated entirely by
development. High-quality foraging areas include irrigated pastures, lightly
grazed grasslands, dry seasonal pools, mowed alfalfa fields, feedlots, and dairies
(Beedy and Hamilton 1999). Lower quality foraging habitats include cultivated
row crops, orchards, vineyards, and heavily grazed rangelands.
Additional methods for refining the model are discussed under model results.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
9
BIRDS
Tricolored Blackbird (Agelaius tricolor)
Model Results
Within the entire study area there is approximately 24.7 acres of modeled
breeding habitat (<0.1% of the entire study area) and 17,706 acres (37% of the
entire study area) of modeled foraging habitat for this species.
Results of the habitat distribution model for suitable breeding are based on two
tiers of analysis. The first tier of analysis is based on application of the
assumptions provided above using geographic information systems (GIS). Using
this analysis several of the ponds within the HCP study area were found to be
unsuitable breeding habitat for the tricolored blackbird. The remaining ponds in
the HCP study area were considered suitable breeding habitat and subject to the
second tier of analysis.
The second tier of analysis involved application of data derived from field
surveys of 68 ponds within the study area. Biologists conducted the pond survey
in September 2003. The purpose of this survey was to provide both physical and
biological data to assess and rank each surveyed pond for breeding habitat
suitability. Of the surveyed ponds, 74% were considered unsuitable habitat
because they did not contain any emergent vegetation (cattails and bulrush) for
nesting. Suitable ponds were then ranked as having high suitability (given a score
of 2) or low suitability (given a score of 1) depending on the amount of tall,
emergent vegetation present. Based on this characteristic, 7 % of the ponds were
considered highly suitable breeding habitat while 19% of the ponds were
considered moderately suitable breeding habitat (Figure 2).
The final step in the second tier of analysis was to extrapolate the findings from
the pond survey (68 pond sample) to all ponds in the study area considered
suitable after the first tier of analysis. The goal of the extrapolation is to
determine the acres of suitable pond breeding habitat in the study area based on
the results of our pond survey. For the tricolored blackbird, our analysis indicates
that 24.5% of the surveyed ponds contain suitable breeding habitat. (For the
extrapolation, all ponds receiving a score of 1 or 2 were considered suitable
breeding habitat.) In addition, because 15 of the 68 surveyed ponds were deemed
unsuitable during the first tier analysis, percent suitability was based on the
remaining 53 ponds. Finally, in order to ensure that the results of our surveys
represent a conservative estimate of suitable habitat, we increased the total
percent of suitable breeding habitat derived from this analysis by 10%. The result
of this multi-tiered analysis is a total of 24.7 acres of suitable breeding habitat
comprised of 12.8 acres of pond habitat and 11.9 acres of emergent marsh
habitat.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
10
Species Range
HCP Study Area
Year-round Range
Summer Range
0
100
MILES
FIGURE 1
Tricolored Blackbird (Agelaius tricolor)
Distribution
Source: Birds of North America 1999
Figure 2 Habitat Distribution Model for Tricolored Blackbird (Agelaius tricolor)
Legend
Sunol
Al a
te
ou
!
(
!
( !
(
!
(
eek
!
(
Sa n
!
(
!
(
!
( !
(
k
!
(
!
(
Reservoir
Secondary Road
Study Area
!
(
!
(
County Line
!
(!
(
(!
SFPUC Ownership
ee
!
(
k
o
Cr
!
(
Primary Road
n
Cr e e k
dia
In
ad
lch
!
(
re e
Ro
s
Stream
!
(
!
((
! !
(
!
(
aC
id a n
yne
Ha
h
Gulc
!
(
!
(
!
(
e !(
rs
!
(
!
(
!
(
!
(
!
(
!
( !
(
p
Primary Foraging Habitat
s
h
st
Co
Sher
!
(
m
lc
!
(
A!(!(!(
p
We
Fremont
!
(
!
(
!
(
Core Breeding Habitat
ia
!
(
!
(
!
(
!
(
!
(!
(
!
(
!
(
!
(
ill
!
(
!
(
(
!
(!
!
(
!
(
!
(
!
(
!
(
!
(
W
!
(
!
(
!
(
!
(
!
(
!
(
!
(
!
(
ek
u
!
(
(
!
(!
!
(
!
(
!
(
!
(
Cr
e
!
(
!
( !
(
!
(
(Note: Core Breeding Habitat in
ponds cannot be seen at
this scale, and are overwritten
by Pond Habitat Suitablity points.)
Va
lle
!
(
!
(
La
!
(
!
(
!
(
!
(
!
(
!
(
!
(
!
(
ni
n A
!
(
Unsurveyed pond
G
d
s Roa
alavera
80
-6
!
(
to
An
Sa
!
!
( (
!
(!
(
!
(
De
l
!
(
!
(
o
!
(
!
(
!
(
ni
!
(
ir
vo
nto
!
(
!
(!
(
!
(!
(!
(
!
(
(
!!
(
( !
!
(!
(
C
y
lle
Va
nol
I
!
(
!
(
!
(
!
(
k
Su
!
(
r ee
!
(
se
r
a
Cr
!
(
Pond Habitat Suitability = High
Pond Habitat Suitability = Moderate
Pond Habitat Suitability = Not Suitable
Unsurveyed Ponds
!
(
Vallecito'
sC
ed
!
(
!
(
!
(
!
(
!
(
m
!
(
(!
(
!
(!
t
!
(
Re
oa
d
s R
ecito
V all
d
oa
o
Ni
le
R
l R
h il
Surveyed Ponds
84
/ R
ke
La
s
Canyon
Fo o
d
ro
80
I-6
e la L a guna
yo d
Ar
n
R
!
(
id
g
L
de
ey
n
ee
Cr
e
!
(
!
(
©
k
!
(
(!
!
(
!
(
!
(
A lame
d a Cr
ee
k
(
!!
(
!
(
!
(
!
(
Oa
!
(
Ca
la
0
I - 68
We
lle r
0
I-88
ve
Re
R oa d
!
(
se
rvo
!
(
!
(
!
(
ir
!
(
P
!
(
!
(
!
(
o
d
oa
!
(
h R
rt
!
(
!
(
!
(
!
(
Ho
ve
!
(
Ma r s
nd
y
!
(
o
!
(
R
!
(
!
(
id
!
(
0
Santa Clara Co.
o
roy
Ar
ras R oa d
r
F elte
Alameda Co.
d g !(
!
( e
0.5
1
1:100,000
Cal a ve
Milpitas
Ri
ra s
!
(
d
Ro a
k
g
Calav
e
er
as
e
Cre
!
(
!
(
!
(
!
(
!
(
k
Mt.
Day
!
(
!
(
2
Miles
BIRDS
Western Burrowing Owl (Athene cunicularia hypugaea)
Western Burrowing Owl
(Athene cunicularia hypugaea)
Status
State:
Bird Species of Special Concern, Second Priority
(California Department of Fish and Game 2008)
Federal:
Migratory Bird Treaty Act (16 USC 703-712)
Critical Habitat:
N/A
Range
The western burrowing owl (Athene cunicularia hypugaea), the western race of
the burrowing owl, is found throughout western North America, west of the
Mississippi River and south into Mexico. Other burrowing owl races occur in
arid, open habitats from the provinces of southern and southwestern Canada to
southern Florida and South America (Haug et al. 1993).
In California, the range of western burrowing owl extends through the lowlands
south and west from north-central California to Mexico, with small, scattered
populations occurring in the Great Basin and the desert regions of the
southwestern part of the state (DeSante et al. 1996) (Figure 1). Burrowing owls
are absent from the coast north of Sonoma County and from high mountain areas
such as the Sierra Nevada and the ranges extending east from Santa Barbara to
San Bernardino. Burrowing owl populations have been greatly reduced or
extirpated from the San Francisco Bay Area (Trulio 1997; Institute for Bird
Populations 2008) along the coast to Los Angeles. The remaining major
population densities of burrowing owls in California are in the Central and
Imperial Valleys (DeSante et al. 1996 Institute for Bird Populations 2008).
The western burrowing owl is distributed over most of Alameda and Santa Clara
Counties. Suitable foraging and breeding habitat for burrowing owl, such as
grasslands, ruderal or open urban areas, vernal pool grasslands, fallow
agricultural fields, and open oak woodlands occur primarily in the eastern
portions of these counties. The potential to extend owl habitat use into suitable
areas is limited by land management practices that reduce ground squirrel
populations, thereby limiting the number of suitable owl nesting burrows.
Occurrences within the HCP Study Area
The western burrowing owl has been observed in two locations in the HCP study
area: northwest of the San Antonio Reservoir and southeast of the San Antonio
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
1
BIRDS
Western Burrowing Owl (Athene cunicularia hypugaea)
Reservoir (T. Koopman pers. comm.). This species likely occurs in potential
habitat throughout the Alameda watershed. Suitable habitat is defined as habitat
that could support burrowing owls based on a general classification of land cover
types (e.g., grassland, vernal pool grassland, grassland pasture) developed for the
HCP. Because a comprehensive survey for the burrowing owl has not been
conducted in the study area, the existing population size and the location
occurrence information are unknown.
Biology
Habitat
Burrowing owls require habitat with three basic attributes: open, well-drained
terrain; short, sparse vegetation; and underground burrows or burrow facsimiles
(Klute et al. 2003). During the breeding season, they may also need enough
permanent cover and taller vegetation within their foraging range to provide them
with sufficient prey, such as small mammals (Haug et al. 1993). Burrowing owls
occupy grasslands, deserts, sagebrush scrub, agricultural areas (including
pastures and untilled margins of cropland), earthen levees and berms, coastal
uplands, and urban vacant lots, as well as the margins of airports, golf courses
and roads.
Burrowing owls select sites that support short vegetation, even bare soil,
presumably because they can easily see over it. Ideal height of grass is a
maximum of 5-inches (Green and Anthony 1989). However, they will tolerate
tall vegetation if it is sparse. Owls will perch on raised burrow mounds or other
topographic relief, such as rocks, tall plants, fence posts, and debris piles, to
attain good visibility (Haug et al. 1993).
The most important habitat consideration for the western burrowing owl is the
availability of underground burrows throughout their life cycle. Although the
owls nest and roost in these burrows, they do not typically create them. Rather,
the owls rely on other animals to dig their burrows. Throughout their range, they
use burrows excavated by fossorial (i.e., digging) mammals or reptiles, including
prairie dogs, ground squirrels, badgers, skunks, armadillos, woodchucks, foxes,
coyotes, and gopher tortoises (Karalus and Eckert 1987). Where the number and
availability of natural burrows is limited (e.g., where burrows have been
destroyed or ground squirrels eradicated), owls will occupy drainage culverts,
cavities under piles of rubble, discarded pipe, and other tunnel-like structures
(Haug et al. 1993).
For western burrowing owls, what constitutes an isolated habitat patch and the
minimum size of a viable patch of habitat (i.e., habitat capable of sustaining a
population over a long time period) are not well documented. These parameters
are affected by habitat quality, the juxtaposition of the site relative to other
suitable habitat, surrounding land uses, and prey availability. Burrowing owls
have been observed in small (i.e., one-acre) lots nearly surrounded by
development; owls will fly through urban areas to forage in nearby areas.
However, the type and minimum extent of development that constitutes a
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
2
BIRDS
Western Burrowing Owl (Athene cunicularia hypugaea)
movement barrier between occupied patches and nearby foraging areas is not
known.
Breeding Habitat Requirements
Like other owls, western burrowing owls breed once a year in an extended
reproductive period during which most adults mate monogamously. Both sexes
reach sexual maturity at one year of age. Clutch sizes vary, and the number of
eggs laid is directly proportional to prey abundance. Clutches in museum
collections in the western United States contain one to 11 eggs (Murray 1976).
The incubation period is 28–30 days; the female performs all the incubation and
brooding and is believed to remain continually in the burrow while the male does
all the hunting. The young fledge at 44 days but remain near the burrow and join
the adults in foraging flights at dusk. (Rosenberg et al. 1998.)
There is little information on lifetime reproductive success (Haug et al. 1993).
Females supplemented with food will have higher reproductive success than
females without supplemented food, which may explain poor reproductive
success in areas with low-quality foraging habitat (Wellicome 1997). Depending
on assumptions about migration, the probability that juvenile burrowing owls
will survive to one year of age (the age of first breeding) has been estimated
between 0.23 and 0.93, and annual adult survivorship between 0.42 and 0.93
(Johnson 1997).
During the breeding season, burrowing owls spend most of their time within
50 to 100 meters (162 to 325 feet) of their nest or satellite burrows (Haug and
Oliphant 1990). During the day, they forage near the natal burrow, where they
find it easy to prey on insects in low, open vegetation. Burrowing owls will nest
in loose colonies, although owls display intraspecific territoriality immediately
around the nest burrow (Haug et al. 1993).
Foraging Requirements
This opportunistic feeder will consume arthropods, small mammals, birds,
amphibians, and reptiles. Insects are often taken during the day, while small
mammals are taken at night. In California, crickets and meadow voles were
found to be the most common food items (Thomsen 1971). In urban areas,
burrowing owls are often attracted to streetlights, where insect prey congregates.
Owls have been detected foraging out to one mile from their burrows and internest distances, which indicate the limit of an owl’s territory, have been found to
average between 61 and 214 meters (198 and 695 feet) (Thomsen 1971; Haug
and Oliphant 1990). Nocturnal foraging can occur up to several kilometers away
from the burrow, and owls concentrate their hunting uncultivated fields, ungrazed
areas, and other habitats with an abundance of small mammals (Haug and
Oliphant 1990).
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
3
BIRDS
Western Burrowing Owl (Athene cunicularia hypugaea)
Demography
The maximum life span recorded for a banded bird in the wild is about 8.5 years
(Rosenberg et al. 1998). Collisions with vehicles are the most common cause of
mortality in this species (Haug et al. 1993). Other sources of owl mortality
include disease, exposure, and human activity around nests (digging or disking)
(Johnson 1992). Predators of burrowing owls include prairie falcon (Falco
mexicanus), red-tailed hawk (Buteo jamaicensis), Swainson’s hawk (Buteo
swainsoni), ferruginous hawk (Buteo regalis), northern harrier (Circus cyaneus),
golden eagle (Aquila chrysaetos), coyote (Canis latrans), and domestic dogs and
cats. Many owls are killed at night by traffic when flying low over roads.
Attempts to exterminate rodents by the use of poisons may also kill burrowing
owls (Rosenberg et al. 1998).
Dispersal
Burrowing owls tend to be resident where food sources are stable and available
year-round. They disperse or migrate south in areas where food becomes
seasonally scarce. In northern California, most owls migrate south during
September and October, though a few are likely resident birds. Southern
California populations are not migratory. In resident populations, nest-site
fidelity is common, with many adults renesting each year in their previous year’s
burrow; young from the previous year often establish nest sites near (<300 meters
or 984 feet) their natal sites (Rosenberg et al. 1998). Burrowing owls in
migratory populations also often renest in the same burrow, particularly if the
previous year’s breeding was successful (Belthoff and King 1997). Other birds in
the same population may move to burrows near their previous year’s burrow.
The spatial requirements of burrowing owls are not well understood. Breeding
pairs of western burrowing owls may require a minimum of 6.5 acres of
contiguous grassland of high foraging quality to persist (California Department
of Fish and Game 1995). However, burrowing owl pairs have been observed in
isolated habitat patches as small as one acre. An area this size does not support
the foraging requirements of most burrowing owls, and individuals occurring at
sites this small must forage offsite. Reproductive success and long-term
persistence in small and isolated habitats are unknown. Although the relationship
between habitat area and population viability of this species is not well
documented, small and isolated habitat patches are not likely to sustain high
reproductive success or long-term persistence (see “Threats” below).
Behavior
Burrowing owls in California typically begin pair formation and courtship in
February or early March, when adult males attempt to attract a mate. Loud “coocooing” at dusk indicates that this stage of the breeding cycle has begun.
Beginning in April, eggs are laid at least one day apart and are incubated by both
adults for about three to four weeks. Young owlets are brooded underground for
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
4
BIRDS
Western Burrowing Owl (Athene cunicularia hypugaea)
another three to four weeks, at the end of which they may sometimes be seen at
the burrow entrance in their natal-down plumage. Nestlings emerge
asynchronously and tentatively in early June. They gradually become bolder,
eventually spending more time outside, near the burrow entrance. During this
period, nestlings can range widely on foot, even before they can fly. The adults
guard their brood tenaciously, attacking intruders if provoked. Older nestlings or
fledglings may move to nearby satellite burrows as the natal burrow becomes
crowded.
Ecological Relationships
Western burrowing owls most commonly live in burrows created by California
ground squirrels (Spermophilis beecheyi). Accordingly, the quality of burrowing
owl habitat in the study area is closely and positively related to the occurrence
and population health of ground squirrels in an area. Burrowing owls and ground
squirrels can co-inhabit the same burrow system (Johnson pers. comm.), but the
frequency with which this occurs has not been measured, and underground
interactions have not been studied. Burrowing owls may compete incidentally
with other predators such as coyote, other owls and hawks, skunks, weasels, and
badgers for rodents and a variety of insects. (Rosenberg et al. 1998.)
Population Trend
Global:
Declining
State:
Declining
Within HCP Unknown
Study Area:
In North America, the burrowing owl is experiencing population declines
throughout the northern half of the Great Plains and population increases in the
northwest interior and some southwestern deserts (Klute et al. 2003). In Canada,
its numbers are rapidly declining; in 1995, the Committee on the Status of
Endangered Wildlife in Canada listed it as endangered. In Mexico, it is officially
considered threatened. The burrowing owl has disappeared from much of its
historical range in California (Klute et al. 2003). The California Department of
Fish and Game indicates that the California population of burrowing owls is
between 1,000 and 10,000 pairs (James and Espie 1997; Rosenberg et al. 1998)
with a declining trend. Nearly 60% of California burrowing owl “colonies” that
existed in the 1980s had disappeared by the early 1990s (DeSante and Ruhlen
1995; DeSante et al. 1997). In the San Francisco Bay Area and the central portion
of the Central Valley from Yolo and Sacramento Counties to Merced County, the
burrowing owl population has declined by at least 65% since 1986. The primary
factors cited for the decline are habitat loss, pesticides, predators, harassment,
reduced burrow availability, and vehicle collisions.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
5
BIRDS
Western Burrowing Owl (Athene cunicularia hypugaea)
Threats
An immediate threat to the burrowing owl is conversion of grassland habitat to
urban and agricultural uses and loss of suitable agricultural lands to development.
Equally important is the loss of fossorial rodents such as prairie dogs and ground
squirrels across much of the owl’s historical habitat. Eradication programs have
decimated populations of these rodents and have therefore disrupted the
ecological relationships on which owls depend—because western burrowing
owls need other animals to dig their burrows, the loss of fossorial rodents limits
the extent of year-round owl habitat.
Another cause of population declines is thought to be pesticide use (especially
organophosphates in southern Canada), but evidence does not clearly indicate
that other contaminants are reducing populations (Gervais et al. 1997). Habitat
fragmentation (Remsen 1978) probably increases foraging distances, making
hunting less efficient and potentially reducing reproductive success.
Fragmentation may reduce the chances that a male owl will attract a mate and
could decrease reproductive success.
The populations of western burrowing owls in the Central Valley and Coast
Ranges, including the Alameda watershed, are threatened primarily by
conversion of habitat to agriculture and control of ground squirrel populations.
Agricultural lands provide much lower quality habitat for burrowing owls than
grasslands. Suitable habitat in agricultural areas is usually restricted to peripheral
bands along the edges of plowed fields. These areas are often frequently
disturbed and subject to loss from agricultural activities. Control of ground
squirrels has reduced the extent and quality of potentially suitable burrowing owl
habitat by reducing the number of suitable nesting burrows. The use of
rodenticides and insecticides may have also reduced prey populations, resulting
in lowered survivorship and reproductive success (Center for Biological
Diversity 2003).
Direct impacts of SFPUC activities in the Alameda Watershed on western
burrowing owl could occur from covered activities, including water supply and
reservoir operations and maintenance (O&M) activities, pipeline maintenance,
and lease and permit easement activities. Specific activities include road
construction, road maintenance that includes shoulder work, bridge replacement
and construction, fence installation and repair, disking or prescribed burning for
vegetation management during the breeding season, recreation, boat launch
construction, vegetation and debris management on dams, pipeline maintenance,
high-traffic livestock areas, and telecom site management. Although recreational
use of the watershed would be carefully controlled, it is possible that some
impacts on western burrowing owls from recreation could occur if a population
became established in an area used for recreation. Indirect impacts on western
burrowing owl could include increased noise during O&M activities that occur
near nest burrows , noise and dust from increased vehicle traffic, and increased
trash from human use, which could attract predators.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
6
BIRDS
Western Burrowing Owl (Athene cunicularia hypugaea)
Data Characterization
According to the California Natural Diversity Database (CNDDB) there are no
occurrences of western burrowing owl in the HCP study area (California Natural
Diversity Database 2008). As noted above, the species has been observed in two
locations within the watershed, though those locations were not formally
documented. There may be instances of other observation of this species that
have also gone undocumented in the past. Habitat for this species is present in the
Alameda watershed, and the western burrowing owl is documented west of the
study area in Fremont and Milpitas (California Natural Diversity Database 2008).
The California Department of Fish and Game was petitioned to list the western
burrowing owl as endangered or threatened under the State Endangered Species
Act in 2003 but that petition was denied (Center for Biological Diversity 2003).
A large amount of peer-reviewed literature is available for the western burrowing
owl. As this species is declining throughout its range, most of the research
studies emphasize nest site selection, passive relocation, use of artificial burrows,
reproductive success, dispersal, and foraging behavior. Common management
efforts employed to conserve existing burrowing owl colonies include prevention
of all disturbances during the nesting season, installation of permanent artificial
burrows, and management of the vegetation around the burrows by mowing or
controlled grazing.
Modeled Species Distribution in HCP Study Area
Figure 2 shows the habitat distribution model for the western burrowing owl
within the 46,700-acre study area.
Model Description
Model Assumptions
1. All valley needlegrass grassland, non-native grassland, and serpentine
bunchgrass grassland land cover types within the HCP study area were
considered suitable breeding and foraging habitat for western burrowing owl.
2. All cultivated fields land cover was considered occasional or limited use
areas for western burrowing owl.
Rationale
Western burrowing owls typically occur in dry, open, shortgrass, treeless plains
often associated with burrowing mammals (Haug et al. 1993). Golf courses,
cemeteries, road allowances within cities, levees, and ruderal borders around
agricultural fields, airports, and vacant lots in residential areas are also used for
both breeding and foraging. Within the Alameda Watershed HCP study area
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
7
BIRDS
Western Burrowing Owl (Athene cunicularia hypugaea)
these habitats are represented by the valley needlegrass grassland, non-native
grassland, and serpentine bunchgrass grassland land cover types.
Burrowing owls are also known to use agricultural areas occasionally when they
are fallow or continually in the margins of these fields. Many patches of ruderal
land-cover type less than 1 acre in size (i.e., less than the minimum mapping
unit) could be used by burrowing owls but were unable to be mapped. To account
for the occasional use by owls of fallow agricultural fields, and the low density
use by owls of patches of ruderal areas, we mapped habitat as “occasional or
limited use” in all cultivated fields land-cover types.
Model Results
Within the entire study area there are 17,328 acres of modeled breeding habitat
(approximately 36% of the study area) and 379 acres (approximately 0.8% of the
study area) of modeled occasional use habitat for this species. Suitable breeding
and foraging habitat is widely distributed throughout the study area. The small
section of the study area that is considered occasional use habitat is located in the
Sunol Valley.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
8
Winter Range
Summer Range
Year-Round Range
HCP Study Area
Winter Range
Summer Range
Year-Round Range
0
100
MILES
FIGURE 1
Western Burrowing Owl (Athene cunicularia hypugea)
Distribution
Source: Adapted from Zeiner et al. 1990a, and Sibley 2000.
Figure 2 Habitat Distribution Model for Western Burrowing Owl (Athene cunicularia hypugaea)
Legend
Ni
le
R
oa
Sunol
d
i ll
th
R
ou
te
84
s
ecito
V all
Vallecito
's C
A la
m
ree
Ro
ad
/ R
Suitable Breeding and Foraging Habitat
Occasional or Limited Use Areas
ke
La
s
Canyon
Fo o
d
ro
80
I-6
e la L a g una
yo d
Ar
k
ed
e ek
De
l
n A
Re
Cr
ee
ni
o
Sa n
to
An
W
k
ill
ia
m
s
G
Stream
u
lc
Primary Road
Reservoir
Secondary Road
Study Area
h
La
st
Co
County Line
p
k
o
ee
rs
Cr
e
n
Cr e e k
p
dia
In
ad
s
SFPUC Ownership
k
Ro
yne
Ha
h
Gulc
lch
re e
id an
aC
Sher
A
We
Fremont
Va
lle
io
I
Sa
on
d
s Roa
alavera
C
y
lle
Va
nol
80
-6
ir
vo
nt
Su
se
r
a
Cr
n
R
id
g
e
L
de
ey
n
ee
Cr
©
k
A lam e
d a Cr
ee
k
Oa
la
Ca
I - 68
We
0
lle r
0
I-88
ve
Ro ad
Re
se
rvo
e
0
Santa Clara Co.
ir
o
rt
Ho
ve
o
roy
Ar
P
y
h R
d
oa
Ma r s
Alameda Co.
dg
0.5
1
1:100,000
ras R oa d
r
F elte
Ri
ra s
Cal a ve
Milpitas
d
Ro a
k
nd
o
R
id
g
Calav
e
er
as
e
Cr e
k
Mt.
Day
2
Miles
FISH
Central Valley Fall-/Late Fall–Run Chinook Salmon (Oncorhynchus tshawytscha)
Central Valley Fall-/Late Fall–Run Chinook Salmon
(Oncorhynchus tshawytscha)
Status
State:
None
Federal:
Species of Concern
(National Marine Fisheries Service 2008)
Critical Habitat:
None
Recovery Planning: None
Taxonomy
Four Chinook salmon (Oncorhynchus tshawytscha) runsfall, late fall, winter,
and springoccur in California. The names of the Chinook salmon runs reflect
the variability in timing of migration and spawning of the adult life stage.
Alameda Creek is encompassed by the fall-/late fall–run Chinook salmon
evolutionarily significant unit (ESU); however, only fall-run Chinook salmon
occur, or have the potential to occur, in Alameda Creek. Consequently, fall-,
winter-, and spring-run Chinook salmon are not discussed here any further.
Chinook salmon occurring in lower Alameda Creek are considered to be part of
the Central Valley fall-/late fall–run Chinook salmon ESU based on genetic
analyses of Chinook salmon returning to other South San Francisco Bay streams
(Stern pers. comm.). The Central Valley fall-/late fall–run Chinook salmon ESU
covers fall- and late fall–run Chinook salmon in the Sacramento and San Joaquin
Rivers and their tributaries (Moyle 2002).
Central Valley fall-run and late fall–run Chinook salmon are important
commercially and recreationally. In 1999, the National Marine Fisheries Service
(NMFS) determined that listing was not warranted and classified the Central
Valley fall-/late fall–run Chinook salmon ESU as a candidate species in 1999;
NMFS transferred this ESU to the newly created species of concern list in 2004
to reflect the fact that they were no longer actively being considered for listing
under the federal Endangered Species Act (ESA) (National Marine Fisheries
Service 2008). Late fall–run Chinook salmon, which experiences low abundance,
is designated as a species of special concern in California (California Department
of Fish and Game 2008). Fall-run Chinook salmon are currently the largest run of
Chinook salmon in the Sacramento River system. Because fall-run Chinook
salmon are the largest of all four runs, they continue to support commercial and
recreational fisheries of significant economic importance.
Species Profiles
SFPUC Alameda Watershed HCP
November 2011
1
FISH
Central Valley Fall-/Late Fall–Run Chinook Salmon (Oncorhynchus tshawytscha)
Range
Chinook salmon occur from northern Japan (Hokkaido) and in Russia from the
Amur River north to the Aanadr River, and from Kotzebue Sound, Alaska to the
California Central Valley (Moyle 2002). In addition, they are often found in the
ocean as far south as southern California. In California, spawning runs are found
from the Central Valley and some tributaries of San Francisco Bay north to the
Smith River in Del Norte County. Over a thousand spawning populations of
Chinook salmon may occur along the North American coast from southeastern
Alaska to California (Healey 1991). Figure 1 shows the distribution of Chinook
salmon in California.
Occurrences within the HCP Study Area
Historical
Archeological sites located within estuary streams tributary to the San Francisco
Bay, including Alameda Creek, have revealed Chinook salmon remains (Leidy
2007). Although these remains have been attributed to fish occurring in San
Francisco Bay and/or the Sacramento–San Joaquin River drainage, it is believed
that Chinook salmon may have entered San Francisco Bay tributary streams,
including Alameda Creek, as strays during years of high abundance (Gobalet et
al. 2004). There appears to be no definitive historical records of Chinook salmon
occurrence in Alameda Creek. However, definitive historical records for Chinook
salmon occurrence exist for nearby lower San Leandro Creek and possibly in
Lake Chabot. A landlocked Chinook salmon population reportedly was present in
Lake Chabot for several years following closure of the dam in 1875, but these
could have been misidentified as Atlantic salmon which were stocked in the
1870s and 1880s (Leidy 2007).
Recent
Beginning in the mid-1980s, reports of Chinook salmon in San Francisco Bay
tributaries increased dramatically (Leidy 2007). The increase in sightings was
coincident with the relocation of the release point of hatchery fish from Central
Valley hatcheries to near Benicia in an attempt to reduce entrainment in the
Central Valley Project and State Water Project pumps, leading to speculation that
hatchery fish were now straying into area streams, including Alameda Creek.
Recent genetic analyses of Chinook salmon adults returning to the Guadalupe
River (Santa Clara County) indicate that most sampled fish are related to Central
Valley and Oregon stocks (Leidy 2007; Garza and Pearse 2008) and appear to
support the hypothesis that Chinook salmon returning to south San Francisco Bay
tributaries are derived from Central Valley hatcheries.
Chinook salmon currently migrate up lower Alameda Creek to spawn but are
blocked from upstream spawning and rearing areas by the San Francisco Bay
Area Rapid Transit (BART) weir and a series of inflatable dams operated by
Species Profiles
SFPUC Alameda Watershed HCP
November 2011
2
FISH
Central Valley Fall-/Late Fall–Run Chinook Salmon (Oncorhynchus tshawytscha)
Alameda County Water District (ACWD) for groundwater recharge.
Consequently, Chinook salmon do not occur currently within the HCP study
area.
Some of the recent occurrences of Chinook salmon in lower Alameda Creek
include the following:

On November 27, 1996, approximately 50 yards downstream of the Southern
Pacific railroad crossing, 20 adult ripe Chinook salmon (six males & 14
females) were rescued from an isolated pool located immediately
downstream of one of the inflatable dams (ACA 2008). The fish were netted
and transported to a free flowing reach upstream beyond the most upstream
inflatable dam near Mission Boulevard in Fremont (ACA 2008).

On December 16, 1996, four Chinook salmon were also observed spawning
near the same location unable to cross the migrational barrier to upper
reaches of Alameda Creek. An additional dead (male) Chinook salmon was
also observed on the shore of the flood control channel beneath the Southern
Pacific railroad crossing. On December 13, 2006, one of the Chinook salmon
observed in the flood control channel in November was stranded and dying
on the cement apron below the BART weir. The 20 pound fish was rescued
and released into deeper water.
Life History and Habitat Requirements
Fall-run Chinook salmon are characterized as being ocean-type Chinook salmon
(as opposed to stream-type), adapted for spawning in lowland reaches of big
rivers and their tributaries (Moyle 2002). Generally, fall-run Chinook salmon
leave the ocean in late summer and early fall to migrate up inland rivers and
streams. Because they are already mature when they leave the ocean, fall-run
Chinook salmon begin spawning within days or weeks of their arrival on
spawning grounds. After emerging from the gravel within a few months, young
Chinook salmon rear in mainstem rivers or estuaries for a short time before
emigrating to the sea in spring (in contrast to stream-type Chinook salmon which
can rear up to one year in freshwater before emigrating to the ocean). This life
history allows for Chinook salmon to exploit habitats that do not support suitable
rearing conditions in summer.
Upstream Migration of Adults
Adult fall-run Chinook salmon migrate into rivers from July through December
and will migrate over considerable distances to return to their natal streams.
Upstream movement is relatively steady, and largely occurs during the day. It is
believed that Chinook salmon use olfactory cues to navigate to their home
streams by tracking the odors of their natal stream which they imprinted on while
they were young. Although most adults return to their natal stream to spawn,
adult fall-run Chinook salmon are known for their relatively high rate of straying,
which allows them in wet years to take advantage of favorable conditions in
streams not typically used for spawning. Because of their large size, mature
Species Profiles
SFPUC Alameda Watershed HCP
November 2011
3
FISH
Central Valley Fall-/Late Fall–Run Chinook Salmon (Oncorhynchus tshawytscha)
status and somewhat more deteriorated condition upon leaving the ocean, fall-run
Chinook salmon typically do not migrate upstream as far as steelhead and other
races of Chinook salmon to spawn.
Adults migrating upstream must have stream flows that provide suitable water
velocities and depths for successful upstream passage (Bjornn and Reiser 1991).
Generally, favorable passage conditions for adult Chinook salmon are achieved
when water depth is greater than 0.8 foot and velocities are less than 8 feet per
second (fps) (Bell 1986 and Thompson 1972 in Bjornn and Reiser 1991).
Spawning and Egg Incubation
The spawning behavior of Chinook salmon is similar to other salmonids. Adult
female Chinook salmon begin digging pits, called redds, in the gravel and cobble
substrate by turning on their side and fanning the substrate with their tail. Stream
currents carry away finer sediments and help to deposit the loosened gravel
downstream of the newly formed pit. The eggs are then fertilized by the male as
the female deposits the eggs in the bottom of the pit. Immediately after the eggs
are fertilized, the female covers the eggs in the process of digging another pit
directly upstream. The spawning process is repeated multiple times until the
female has deposited all of her eggs. Eggs hatch in approximately 6–12 weeks
depending on water temperatures, and newly emerged larvae remain in the gravel
for another 2–4 weeks until the yolk is absorbed (Moyle 1976; Beauchamp et al.
1983; Allen and Hassler 1986). Successful spawning and egg incubation require
adequate quantity and quality of flow, water temperature, and substrate.
Water depth, velocity, and quality are determined by stream flow. Higher stream
flows often results in greater spawning area provided that inundated spawning
areas have the right combination of depth, velocity, and gravel composition.
Water depth influences spawning site selection (Raleigh et al. 1986; Bjornn and
Reiser 1991). Minimum water depths at redd areas vary with fish size and water
velocity because these variables affect the depth necessary for successful digging
(Healey 1991). Although water depth at least deep enough to cover the fish
during spawning is optimum, Chinook salmon have been observed to spawn in
water ranging in depth from as little as 5 cm (2 inches) to as deep as 720 cm
(23.6 feet) (Burner 1951 and Vronskiy 1972 in Healey 1991; Bjornn and Reiser
1991).
Flow velocity also affects spawning site selection and a wide range of water
velocities are used by spawning adults. Adults have been observed to spawn in
water velocities of 30–189 cm/second (0.98–6.2 fps) (Healey 1991). Studies in
northern California found that Chinook salmon from the Yuba and Sacramento
Rivers preferred velocities of 47.2–89.9 cm/second (1.55–2.95 fps) and 27.4–
82.3 cm/second (0.9–2.7 fps), respectively (California Department of Fish and
Game 1991).
Water temperatures can limit the geographic range in which Chinook salmon can
successfully spawn and rear. Maximum survival of incubating eggs and yolk-sac
larvae occurs at water temperatures between 41ºF and 57ºF (Beauchamp et al.
Species Profiles
SFPUC Alameda Watershed HCP
November 2011
4
FISH
Central Valley Fall-/Late Fall–Run Chinook Salmon (Oncorhynchus tshawytscha)
1983; Allen and Hassler 1986; Raleigh et al. 1986). As water temperature
exceeds 57ºF, incubating eggs begin to suffer increased mortality; water
temperatures above 61ºF are lethal.
The quality of spawning habitat is also correlated with intra-gravel flow. Low
intra-gravel flow may lead to insufficient dissolved oxygen, contribute to the
growth of fungus and bacteria, and result in high levels of metabolic waste.
A high percentage of fine sediment in gravel substrates can substantially limit
intra-gravel flow, affecting the amount of spawning gravel available in the river
(Healey 1991). Optimal gravel conditions for spawning include substrates
ranging in size from 0.5 to 4.0 inches, with less than 5–10% fine sediments
measuring 0.3 cm (0.12 inch), or less, in diameter (Raleigh et al. 1986; Bjornn
and Reiser 1991). Alevins can also have difficulty emerging when fine sediments
exceed 30–40% of gravel volume (Phillips et al. 1975 in Bjornn and Reiser 1991;
Waters 1995).
Rearing
After emerging from the gravel, Chinook salmon fry tend to seek shallow,
nearshore habitat with slow water velocities and move to progressively deeper,
faster water as they grow. Juveniles are opportunistic feeders and eat a wide
variety of terrestrial and aquatic insects. Juveniles typically rear in fresh water for
up to 5 months before migrating to sea.
Rearing habitat quality for salmonids is defined by environmental conditions
such as water temperature, dissolved oxygen, turbidity, substrate, area, water
velocity, water depth, and cover (Bjornn and Reiser 1991; Healey 1991; Jackson
1992). Environmental conditions and interactions among individuals, predators,
competitors, and food sources determine habitat quantity and quality and the
productivity of the stream (Bjornn and Reiser 1991). Rearing habitat for juvenile
Chinook salmon includes riffles, runs, pools, and inundated floodplains.
Use of floodplain habitat by juvenile Chinook salmon has been well documented
(California Department of Water Resources 1999; Sommer et al. 2001).
Floodplain habitat provides favorable rearing habitat for juvenile Chinook
salmon (Sommer et al. 2001). The faster growth rate in floodplains may be
attributed to increased prey consumption associated with greater availability of
drifting invertebrates and warmer water temperatures. Invertebrate production on
the floodplain may be stimulated by availability of detritus in the food web,
available habitat for benthic invertebrates, and a relatively long hydraulic
residence time, which reduces the rate at which nutrients and drifting
invertebrates are flushed out of the system.
Juvenile Chinook salmon may tolerate water temperatures of 32ºF to 75ºF, but
the optimal range for survival and growth, provided an adequate food supply
exists, is from 54ºF to 64ºF (Raleigh et al. 1986). Juveniles require relatively cool
water temperature to complete the parr-smolt transformation and to maximize
their saltwater survival. Successful smolt transformation deteriorates at
temperatures of 17–23ºC (62.6–73.4ºF) (Myrick and Cech 2001).
Species Profiles
SFPUC Alameda Watershed HCP
November 2011
5
FISH
Central Valley Fall-/Late Fall–Run Chinook Salmon (Oncorhynchus tshawytscha)
Reproduction
Central valley fall-run Chinook salmon spawn from late September to December
or January, with peak spawning taking place during late October and November
when water temperatures decrease (Moyle 2002).
Fall-run Chinook salmon typically return to spawn as 3-, 4-, and 5-year-olds,
although a smaller proportion of the run return as 2-year-olds. Once they reach
their home stream, fall-run Chinook salmon spawn within days or a few weeks
upon their arrival to spawning grounds. Unlike steelhead, which may survive to
spawn again, all Chinook salmon adults die after spawning.
Individual female Chinook salmon produce from approximately 2,000 to
17,000 eggs, with larger fish typically producing the most eggs (Moyle 2002).
Sacramento River fall-run Chinook salmon produce about 5,500 eggs on average
(Moyle 2002).
Mature female Chinook salmon exposed to water temperatures above 60ºF for
prolonged periods experience poor survival and produce less viable eggs than
females subjected to lower water temperatures (Hinze 1959).
Smolt Out-Migration
Juvenile fall-run Chinook salmon start migrating downstream from January
through June, shortly after emerging from their redds. As juveniles begin to
grow, they gradually begin to undergo physiological, morphological, and
behavioral changes of smolting that prepares them for ocean life. Juveniles
undergoing the smoltification process experience a wide range of morphological
and behavioral changes, including changes in coloration (becoming more
silvery), weight-to-length ratio, body shape, and a tendency to exhibit schooling
and migrational behavior.
As Chinook salmon fry grow, their tolerance to salinity gradually increases.
Consequently, some Chinook salmon fry enter estuaries without first undergoing
the morphological changes associated with smolting (Allen and Hassler 1986).
The transformation of juveniles into smolts is affected by fish size, growth rate,
and environmental factors such as temperature, photoperiod, and lunar cycle
(Ewing et al. 1979 and Grau 1981 in Allen and Hassler 1986). Because the
smoltification process is often incomplete as juveniles begin migrating
downstream, exposure to excessive water temperatures can cause juveniles to fail
to complete the smoltification process. Water temperatures less than or equal to
55ºF are considered optimal for juvenile emigration (Allen and Hassler 1986).
Species Profiles
SFPUC Alameda Watershed HCP
November 2011
6
FISH
Central Valley Fall-/Late Fall–Run Chinook Salmon (Oncorhynchus tshawytscha)
Ecological Relationships
Chinook salmon play an important role in the behavior and ecology of numerous
terrestrial consumers. Many animal species, including birds and mammals, feed
on live adults or decaying carcasses and are attracted to streams in which
Chinook salmon are spawning. In addition, because of their large size and time
spent as predators in the nutrient-rich ocean, Chinook salmon are an important
pathway for introducing marine derived nutrients such as carbon, nitrogen,
phosphorus, and other micronutrients, into inland freshwater and terrestrial
ecosystems. As they decay, salmon carcasses enhance stream productivity
through the release of the marine derived nutrients, that become available to
aquatic invertebrates (and important food source for fish, including juvenile
Chinook salmon) and other aquatic life.
Juvenile Chinook salmon are vulnerable to predation by a wide variety of
animals, including birds, mammals, and native and nonnative fish species. Garter
snakes also prey on juvenile Chinook salmon.
Population Status and Trends
Global:
Stable, but population numbers vary from year to year
(Pacific Fishery Management Council 2006).
State:
Declining, current spawning escapement levels below
conservation goal (Pacific Fishery Management Council 2008).
Within HCP Absent, but current conservation measures may provide access to
Study Area: upper portions of Alameda Creek and could promote selfsustaining populations, depending on availability of suitable
habitats for adult spawning, egg incubation, juvenile rearing and
smolt emigration.
The most abundant populations of fall-run Chinook salmon occur in the
Sacramento, Feather, Yuba, and American Rivers (Mills and Fisher 1994).
Populations also occur in smaller tributaries of the Sacramento River and in
tributaries of the San Joaquin River. Fall-run Chinook salmon have a relatively
large hatchery component, averaging more than 25,000 adults. Natural spawners
average about 200,000 adults for the Sacramento and San Joaquin systems
(Moyle 2002). Currently, the Pacific Fishery Management Council (PFMC) has
an escapement conservation goal of 122,000–180,000 hatchery and naturally
produced fish for the Sacramento River and its tributaries. For 2007 (the last year
adult spawning escapement numbers are available), the spawning escapement of
Sacramento River fall-run Chinook salmon was estimated to be 88,000 adults,
lower than expected and well below the current escapement conservation goal
(Pacific Fishery Management Council 2008). Because jack returns in 2007 were
an order of magnitude lower than the historic lowest return, adult escapement for
2008 is also forecasted to be low. The continuing declining trend in adult
escapement since the recent peak escapement of 775,000 spawners in 2002,
combined with the forecast of even lower returns for 2008, prompted the PFMC
to adopt the most restrictive salmon fishery regulations for commercial and
Species Profiles
SFPUC Alameda Watershed HCP
November 2011
7
FISH
Central Valley Fall-/Late Fall–Run Chinook Salmon (Oncorhynchus tshawytscha)
recreational fishers in the history of the West coast (Pacific Fishery Management
Council 2008).
Threats
Degradation and loss of habitat have contributed substantially to the decline of
Chinook salmon. Shasta and other dams blocked access to historic spawning and
rearing habitat. Other factors adversely affecting abundance include modification
of water temperatures resulting from reservoir operations, harvest, entrainment in
diversions, loss of floodplain connectivity, predation by nonnative species,
interaction with hatchery stock, disease, pollution, loss of riparian areas, siltation,
and natural factors including ocean conditions (Moyle 2002).
Low flows limit habitat area and adversely affect water quality by elevating
water temperatures and depressing dissolved oxygen; these conditions stress
incubating eggs and rearing juvenile fall-run Chinook salmon. Low flows may
affect migration of juvenile and adult Chinook salmon because decreased depths
can inhibit adult passage, and reduced velocity can impede the downstream
movement of juveniles. Low flows in combination with water diversions may
result in higher entrainment losses in unscreened diversions because a greater
proportion of flow is diverted.
Dam and reservoir operations and diversion of water for water supply alter the
natural hydrologic regime in the Alameda Creek watershed and would have the
greatest effect on fall-run Chinook salmon abundance. The primary hydrologic
effect of reservoir operation is the reduction in peak and fall/winter/spring base
flows during periods of high reservoir inflows (i.e., during the wet season).
Other covered activities potentially affecting Chinook salmon abundance include
dam releases for valve maintenance and land-use practices (e.g., road
maintenance and construction, livestock grazing) that affect the delivery of fine
sediments to aquatic habitats.
Data Characterization
Information on the species’ presence in lower Alameda Creek is generally
qualitative and limited to incidental observations by the public, agency staff, and
fishery professionals. However, this information is sufficient to determine
potential habitat use throughout the study area, particularly in the upper reaches
of the creek, once upstream passage is restored at several impassable barriers
(e.g., BART weir, inflatable rubber dams) in lower Alameda Creek. These
barriers, insufficient streamflow and high water temperatures are the primary
obstacles keeping Chinook salmon from establishing self-sustaining populations
in the Alameda Creek watershed.
Species Profiles
SFPUC Alameda Watershed HCP
November 2011
8
FISH
Central Valley Fall-/Late Fall–Run Chinook Salmon (Oncorhynchus tshawytscha)
Existing Conservation Actions in the Study Area
The Fish Passage Improvement Program is a multiagency effort to assist
anadromous fish populations to migrate past barriers in the Alameda Creek
watershed. The San Francisco Public Utilities Commission (SFPUC) removed
the Sunol and Niles Dam in 2005. SFPUC is also working extensively to improve
habitat conditions for all fishes in the upper Alameda Creek watershed through
their aquatic resources monitoring program, as part of their agreement with the
California Department of Fish and Game (DFG) in the 1997 memorandum of
understanding.
The Alameda County Flood Control District (ACFCD) and the ACWD are
working together to design a fish ladder to allow migratory fish to bypass the
BART weir and the adjacent inflatable water supply dam in lower Alameda
Creek. The goal was to have the fish ladder completed by 2010.
In 2007, the ACWD installed four state-of-the-art rotating fish screens initially
intended to assist out-migrating juvenile steelhead from diversion entrainment.
Subsequently, these screens will also benefit Chinook salmon juveniles as well.
The agency installed an additional fish screen at the Bunting Pond in 2009. In
addition, the ACWD removed the lower rubber dam and notched the foundation
weir in the summer of 2009.
The Alameda Creek Fisheries Restoration Workgroup (ACFRW) is a
collaboration of 12 local, state and federal agencies working together for
anadromous fish restoration in the Bay Area. Removal of the Niles and Sunol
Dams are just the beginning of their extensive efforts to remove instream fish
passage barriers, and planning is underway to remove three additional dams. The
ACFRW is also seeking funding for phase two of the fish passage projects in
lower Alameda Creek. Phase two projects include construction of a fish ladder
around the drop structure and middle rubber dam (a 22 foot drop), a fish ladder at
the upper rubber dam (a 13 foot drop), and installation of fish screens at the
remaining ACWD diversion facilities (Alameda Creek Alliance 2008).
The Alameda Creek Alliance (ACA) is a community watershed organization
dedicated to protecting and restoring natural ecosystems of Alameda Creek,
including dam removal, fish passage facilities, and fish screens along 40 river
miles of riverine habitat. Their primary goal is to restore anadromous fish
populations in Alameda Creek by the removal or modification of instream
barriers in the lower watershed. In the past, the ACA has received permission on
an annual basis from the DFG and NMFS to move blocked or stranded fish
upstream. They are also working towards fish passage past the Pacific Gas and
Electric Company (PG&E) pipeline crossing (armored gas line crossing), and the
replacement of existing culverted road crossings with bridges. (Alameda Creek
Alliance 2008a, 2008b.)
Species Profiles
SFPUC Alameda Watershed HCP
November 2011
9
FISH
Pacific Lamprey (Entosphenus tridentatus)
Pacific Lamprey (Entosphenus tridentatus)
Status
State:
None
Federal:
Species of Concern
Critical Habitat:
Not designated
Range
Pacific lamprey (Entosphenus tridentatus, formerly Lampetra tridentata) is
found in Pacific coast drainages from Hokkaido Island, Japan, through Alaska
and south to Rio Santo Domingo in Baja California. Their distribution south of
San Luis Obispo County, California, is scattered or disjunct, although there are
regular runs of adults in the Santa Clara River in Ventura County (Moyle 2002).
Occurrences within the HCP Study Area
Leidy (1984) lists five collection records for Pacific lamprey from Alameda
Creek between 1955 and 1976. All collections were from the Niles Canyon area.
More recently, lamprey ammocoetes (the larval life stage) were collected in 1998
through 2006 at several sites in Alameda Creek between Niles Canyon and the
confluence with Calaveras Creek (Trihey & Associates 2001; San Francisco
Public Utilities Commission 2002a, 2002b, 2002c, 2007a, 2007b, 2007c, 2007d,
2007e). These collections are important in that they demonstrate how lamprey
can pass a number of existing barriers in Alameda Creek that prevent access by
other anadromous fish noted for their leaping abilities (e.g., steelhead and
Chinook salmon). It should be noted that, although these observations are
assumed to be Pacific lamprey ammocoetes, taxonomy is inconclusive, and it is
possible that some of these observed ammocoetes are actually river lamprey (L.
ayresi) and/or western brook lamprey (L. richardsoni) as the ammocoetes of
these three species are nearly indistinguishable from one another (69 FR 247).
Biology
Habitat
Pacific lamprey is anadromous, with a free-swimming parasitic or predatory
marine adult stage and a benthic filter-feeder freshwater immature stage.
Spawning takes place in higher-gradient, cool-water streams with gravel/cobble
beds. In headwater streams and the lower reaches of larger watercourses,
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
1
FISH
Pacific Lamprey (Entosphenus tridentatus)
ammocoetes depend on complex channel structures (e.g., channel meanders,
gravel bars, alcoves, backwaters, and large wood) to create environments that are
suitable for burrowing and filter feeding (Torgersen and Close 2004:627).
Presumably, suitable habitats include areas with water velocities that are fast
enough to provide a steady influx of food while at the same time slow enough to
promote the deposition of fine sediments for burrowing (Torgersen and Close
2004:625). Pool habitats are believed to provide more favorable conditions for
ammocoetes because they are more likely to contain fine sediments, compared to
riffle margins, and their structural complexity may afford ammocoetes with
greater protection from flow-inducted stresses (Torgersen and Close 2004).
Foraging Requirements
The adult predatory phase occurs in the ocean; except for landlocked populations,
adults in freshwater do not feed. Ammocoetes are not predatory but feed on
organic detritus and algae gathered from the surface of the substrate.
Reproduction
In central California, adults enter freshwater to spawn primarily between early
March and late June, typically during periods of higher flow during winter runoff
(Moyle 2002). They are known to migrate over 400 kilometers upstream in larger
river systems and can pass many barriers to other fish by using their sucker
mouths to attach to the surface and rest between bouts of exerted swimming.
They spawn in gravel/cobble substrate in relatively swift currents, often in
similar habitat as that of steelhead and salmon. Both sexes assist in the
construction of a pit in the substrate, moving gravel or cobbles by attaching their
mouth to the rock and swimming vigorously in the current. The resulting nest is
not unlike that of a steelhead or salmon but tends to be shallower and more
circular, often with stones piled completely around the margin of the nest. The
eggs are fertilized over the nest and drift into the gravel. The adults will typically
loosen rocks upstream of the nest, causing the eggs to be buried under a layer of
silt, sand, and gravel. Usually both sexes die after spawning, although some
adults will occasionally survive and spawn again the next year. Embryos hatch in
about 19 days at 15°C (Moyle 2002). Based on laboratory studies, survival of
embryological and early larval stages appears to be optimal over the range 10–
18°C, with a sharp decline in survival at 22°C (Meeuwig et al. 2005). The
ammocoete stage lasts 2 to 7 years (Moyle 2002). After a short time in the nest,
young ammocoetes (larvae) swim up into the current and drift downstream to
quieter channel-margin, pool, or backwater habitats where they burrow tail first
in sand or silt substrates. Over the course of their freshwater larval stage,
ammocoetes often move around, typically at night. As ammocoetes
metamorphose into the juvenile phase (they are called macropthalmia at this
point), they begin to develop eyes and teeth and become free swimming.
Metamorphosis occurs gradually over several months and marks the beginning of
their maturation into adults; they soon emigrate to the ocean where they
parasitize a variety of marine and anadromous fish species.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
2
FISH
Pacific Lamprey (Entosphenus tridentatus)
Demography
The oceanic adult stage is known to last 3 to 4 years off British Columbia but
may be shorter in southern waters off California (Moyle 2002). The freshwater
ammocoete stage is thought to last 2 to 7 years. At a size of about 14 to 16
centimeters, ammocoetes transform to a preadult stage (called macropthalmia)
with large eyes, a sucking disc, silver sides and blue backs, and an alteration in
their physiology that allows transition to seawater. At this stage, they begin their
downstream migration, presumably in winter and spring (Moyle 2002).
Ecological Relationships
Adults prey on a variety of ocean fishes, including salmon and flatfish. They
attach to the fish and rasp through the skin with their bony mouth parts, feeding
primarily on bodily fluids. Many fish survive this process as is evident from the
high frequency of scarring observed in some salmon fisheries. Adult lamprey
may be important in the diet of sharks and sea lions (Moyle 2002). Ammocoetes
feed primarily on organic detritus collected off the stream’s substrate. Their
cryptic lifestyle likely limits their susceptibility to predation, although they are
known to move about at night. After transforming and beginning their
downstream migration, they are likely more vulnerable to predators.
Population Trend
Global:
Secure
State:
May be reduced from historical abundance; eliminated from
some areas where formerly found
Within HCP Unknown, but may be stable in some areas
Study Area:
Threats and Reasons for Decline
Pacific lamprey still appear to be present in most of their native range, though
anecdotal evidence indicates that abundance is reduced in many areas and some
large runs have nearly disappeared. They are usually absent from highly altered
or polluted streams and have been eliminated from many urbanized streams in
the southern part of their range (Moyle 2002).
Because of their extended freshwater period, habitat degradation is likely to be
the greatest single threat to Pacific lamprey. Threats potentially impacting
lamprey ammocoetes and juveniles include excessive sedimentation, water
quality degradation, stream and floodplain degradation, dewatering, predation
from nonnative species, and entrainment in unscreened water diversions, and
impingement on fish screens (69 FR 247, December 27, 2004; U.S. Fish and
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
3
FISH
Pacific Lamprey (Entosphenus tridentatus)
Wildlife Service 2010). Adult lampreys are threatened by many of the same
issues facing steelhead and Chinook salmon, in addition to being harvested from
the redds for bait (Hannon and Deason 2008). Artificial structures such as dams,
road culverts, and water diversions can impede or block upstream migrations by
adult lamprey. There is evidence that fish ladders designed to pass salmonids
may impede the passage of adult lamprey (69 FR 77163, December 27, 2004;
U.S. Fish and Wildlife Service 2010). Based on laboratory studies, elevated
water temperatures may also cause adverse effects on spawning, egg incubation,
and ammocoete development.
Model results for steelhead and Chinook salmon indicate that San Francisco
Public Utilities Commission’s (SFPUC’s) covered activities will decrease habitat
for these species relative to the template condition. This change is expected to
decrease population conditions for Pacific lamprey in the Alameda Creek
watershed, absent implementation of best management practices (BMPs) and
other conservation actions developed as part of the conservation strategy.
Diversion of water for water supply and dam and reservoir operations are
expected to have the greatest effect on Pacific lamprey and their habitat, while
maintenance activities (e.g., valve maintenance) could also lead to direct impacts
through nest scour and displacement and/or stranding of ammocoetes. Impacts
from recreation are possible, but are likely to be relatively minor. Indirect effects
may occur from water-quality degradation (turbidity, sedimentation, pollutants)
associated with soil disturbance (road and bridge construction, road maintenance,
and livestock grazing), and herbicide and pesticide application at golf courses,
and these effects may be more pronounced for ammocoetes than juvenile
salmonids because of their more sedentary nature. Effects related to water-quality
degradation, however, are expected to be small because BMPs will be
implemented to protect water quality.
Data Characterization
Data for lamprey are relatively incomplete since ammocoetes live within the
substrate and are not easily captured or quantified using standard sampling
methods, such as netting (e.g., seining) and trapping, and are not often observed
during snorkel surveys. Lampreys have received little scientific attention, and
there is uncertainty regarding their status and biology. U.S. Fish and Wildlife
Service (USFWS), through its Pacific Lamprey Conservation Initiative
(http://www.fws.gov/pacific/fisheries/sp_habcon/lamprey/index.html), is
currently soliciting input from interested parties to collect data and conduct
research that will enhance the understanding of lamprey and to identify their
conservation needs. The goal of the initiative is to develop a Pacific Lamprey
Conservation Plan to facilitate restoration of Pacific lamprey populations and
improvement of their habitat.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
4
Species Range
HCP Study Area
"Probable" Species Range
0
100
MILES
FIGURE 1
Pacific lamprey (Lameptra tridentata)
Distribution
Source: UC Davis ICE 2003
FISH
Central California Coastal Steelhead (Oncorhynchus mykiss)
Central California Coast Steelhead
(Oncorhynchus mykiss)
Status (Anadromous Form)
State:
None
Federal:
Threatened (Central California Coast Steelhead distinct
population segment [DPS])1
Critical Habitat:
Designated
Taxonomy
Steelhead and rainbow trout (Oncorhynchus mykiss) represent distinct life-history
forms of the same species. Steelhead are the anadromous (i.e., seagoing) form of
rainbow trout; those that do not migrate to the ocean and remain in freshwater for
the duration of their life are referred to as “resident” rainbow trout. Both forms
can exist within the same population with no observable genetic distinction.
Because of these similarities, both forms are discussed in this section.
Steelhead parr (pre-migrant rearing juveniles) are visually and behaviorally
indistinguishable from non-anadromous rainbow trout parr. Not only can
steelhead and resident fish interbreed where they co-occur, but the two forms can
also produce offspring that express the alternate life history form. For example,
steelhead offspring may mature and spawn in the stream before or without
migrating to the ocean while resident rainbow trout offspring may undergo
smoltification and migrate to the ocean. The relationship between these two lifehistory forms of rainbow trout is poorly understood. Only the anadromous form
(i.e., steelhead), and resident rainbow trout that co-occur with the steelhead, are
currently subject to the federal threatened listing (50 CFR Parts 223 and 224;
January 5, 2006). Resident rainbow trout populations that exist above longstanding natural barriers or artificial impassable barriers are not included in the
listing. The National Marine Fisheries Service (NMFS) has conducted a status
review of listed salmonids, evaluating the need for extending protections to
genetically linked resident rainbow trout populations. In its final rule, NMFS
concluded that the resident O. mykiss populations of Upper Alameda Creek and
the Livermore–Amador Valley are not considered part of the listed distinct
population segments (71 FR 841, January 5, 2006).
1
Until recently, NMFS used evolutionarily significant unit, or ESU, to describe populations of steelhead that are
considered distinct for purposes of conservation; NMFS now uses distinct population segment, or DPS, which
generally is synonymous with ESU.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
1
FISH
Central California Coastal Steelhead (Oncorhynchus mykiss)
Range
The historical range of Central California Coast steelhead (CCC steelhead)
includes coastal streams from the Russian River, in Sonoma County, south to and
including Soquel Creek in Santa Cruz County. This includes streams tributary to
the San Francisco, San Pablo, and Suisun Bays eastward to Chipps Island at the
confluence of the Sacramento and San Joaquin Rivers and streams tributary to
Suisun Marsh (71 FR 849, January 5, 2006). Two artificial propagation programs
also are considered to be part of the CCC steelhead distinct population segment
(DPS): the Don Clausen Fish Hatchery in the Russian River drainage, and the
Kingfisher Flat Hatchery/Scott Creek (Monterey Bay Salmon and Trout Project)
steelhead hatchery programs (71 FR 849, January 5, 2006). CCC steelhead are
still present in most of the coastal streams in their historical range, though
abundance may be reduced and/or distribution within individual basins may be
restricted. Figure 1 provides a map of the CCC steelhead DPS.
Occurrences within the HCP Study Area
Occurrence of steelhead and rainbow trout in Alameda Creek was summarized
recently in Gunther et al. (2000). Historically, the Alameda watershed supported
anadromous steelhead. Photographic records appear to document this; however,
no reliable scientific records exist of the size of steelhead spawning populations
or the distribution of spawning and rearing areas that once occurred in the
watershed. Rainbow trout have been documented above Calaveras Reservoir on
several occasions since 1905, based on collections from Arroyo Hondo, Isabel,
and Smith Creeks. Although there may have been some stocking of exotic trout
in these streams in the past, the present self-sustaining populations are most
likely derived from CCC steelhead that were isolated in the upper part of the
drainage by natural processes or by construction of Calaveras Dam between 1916
and 1925. Self-sustaining rainbow trout populations also exist in streams of the
San Antonio watershed above San Antonio Reservoir. The occurrence of rainbow
trout populations above reservoirs on former steelhead streams has been observed
at numerous other locations, including in San Leandro Reservoir tributaries
(Alameda County) and San Pablo Creek above San Pablo Reservoir (Contra
Costa County). Trout populations isolated above dams often adopt an adfluvial
life-history, spending most of their lives in the reservoirs and migrating to
tributary streams to spawn.
Historical records indicate that steelhead and/or rainbow trout have also been
collected or observed in other parts of the watershed. Follett (pers. comm.)
reported observing “large young” trout immediately below a dam in Niles
Canyon in 1927. Follett also collected juvenile rainbow trout at two locations in
Stonybrook Canyon in 1955 and “half grown” rainbow trout at pools opposite
Niles nursery in 1957. Skinner (1962) reported steelhead and/or rainbow trout in
Alameda Creek, Arroyo Mocho Creek, Arroyo del Valle Creek, and Arroyo de la
Laguna Creek. In 1976, the California Department of Fish and Game (DFG)
collected multiple age classes of rainbow trout, including young-of-the-year,
from three locations in Arroyo Mocho Creek, and in Stonybrook Canyon (Leidy
1984). Scoppettone and Smith (1978) reported steelhead and/or rainbow trout in
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
2
FISH
Central California Coastal Steelhead (Oncorhynchus mykiss)
Alameda Creek in the vicinity of Ohlone Park and in Arroyo Mocho Creek. Gray
(pers. comm.) documented the occurrence of young-of-year rainbow trout in
Alameda Creek just upstream of its confluence with Calaveras Creek in 1983,
and again in 1987.
More recently, Alameda County documented the presence of reproducing
populations of rainbow trout in Arroyo Mocho and two tributaries of Alameda
Creek: Welch Creek and Pirate Creek (Alameda County 1999). Reproducing
trout populations have also been observed in Stonybrook Creek and Alameda
Creek in Sunol Regional Park based on sampling conducted by the East Bay
Regional Park District (Gunther et al. 2000). In addition, San Francisco Public
Utilities Commission (SFPUC) has documented the occurrence of wild
populations of rainbow trout in Arroyo Hondo upstream of Calaveras Reservoir,
Alameda Creek upstream and downstream of the Alameda Creek Diversion Dam,
and La Costa and Indian Creeks upstream of San Antonio Reservoir (San
Francisco Public Utilities Commission 2004, 2005a, 2006, 2007). These recent
documented occurrences of rainbow trout in Alameda Creek and its tributaries
suggest that current habitat conditions in the watershed continue to support
spatially distributed, self-sustaining populations of rainbow trout.
Although adult steelhead do not have access to the upper Alameda Creek
watershed, there have been well-documented reports of steelhead being sighted
in the Lower Alameda Creek channel below the San Francisco Bay Area Rapod
Transit (BART) weir, an impassable barrier adjacent to the middle inflatable dam
operated by the Alameda County Water District (ACWD). Sightings of steelhead
downstream of the BART weir were frequently reported in 1998, 1999, 2000,
and 2002 (Gunther et al. 2000). Beginning in 1998, some of these fish were
captured by citizens' groups and released at the mouth of Niles Canyon upstream
of ACWD’s most upstream inflatable diversion dam. In 1999, two released fish
were fitted with radio transmitters and one of them, a gravid female, was tracked
into Stonybrook Creek, a tributary entering Alameda Creek in Niles Canyon.
Some of the steelhead unable to pass the BART weir have been observed to
spawn in Alameda Creek downstream of the middle inflatable dam. In 1998,
fertilized eggs were collected from the stream bottom immediately downstream
of the BART weir and raised in aquaria. The eggs hatched successfully and the
resulting fry were released in Alameda Creek in Sunol Park (Gunther et al.
2000).
Currently, there are three rainbow trout put-and-take (i.e., recreational) fisheries
in the Alameda Creek watershed that are variously supported through stocking
programs managed by DFG and East Bay Regional Park District (EBRPD): Lake
Del Valle near Livermore, Shadow Cliffs Regional Park near Pleasanton, and the
Quarry Lakes Regional Recreational Area near Union City/Fremont. Currently,
hatchery-raised rainbow trout are used to support these recreational fisheries.
Genetic studies show that rainbow trout currently found in Calaveras Reservoir
are most closely related to trout in upper Alameda Creek and nearby San Antonio
Reservoir and are more closely related to coastal steelhead than to hatchery trout
(Nielsen 2003).
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
3
FISH
Central California Coastal Steelhead (Oncorhynchus mykiss)
As mentioned earlier, the listing designation currently applies only to naturally
spawned populations of anadromous forms of O. mykiss and co-occurring
‘resident’ rainbow trout residing below long-term naturally occurring or artificial
impassable barriers. All potential habitat currently in the HCP study area is
upstream of existing artificial impassable barriers. Removal of these barriers
would presumably result in inclusion of suitable habitat upstream within the
critical habitat designation and the existing resident rainbow trout populations
below the reservoirs in the CCC steelhead DPS once access to these habitats is
provided for anadromous adults.
Biology
Habitat
Rainbow trout have a complex life history and may follow a variety of lifehistory patterns, including some that may exhibit anadromy (i.e., migrate to the
ocean to mature as adults) or freshwater residency (i.e., are not migratory and
reside their entire life in freshwater). The relationship between these two lifehistory forms when they occur together is poorly understood. Intermediate lifehistory patterns also exist and include fish that migrate within the stream
(potamodromous), fish that migrate only as far as estuarine habitat, and fish that
migrate to near-shore ocean areas. These life-history patterns do not appear to be
genetically distinct, and individuals exhibiting different life-history patterns have
been observed interbreeding (Shapovalov and Taft 1954). Steelhead habitat
requirements are associated with distinct life-history stages, including migration
from the ocean to inland spawning and rearing habitats, spawning and egg
incubation, rearing, and seaward migration of smolts and spawned adults. Habitat
requirements and life-history timing for steelhead can vary widely over their
natural range.
Because little life-history information exists for steelhead in the Alameda Creek
watershed, the following life-history information is summarized from
Shapovalov and Taft (1954), who conducted one of the most comprehensive
investigations of steelhead life history during studies conducted on Waddell
Creek in Santa Cruz County.
Upstream Migration of Adults
Adult steelhead in this DPS leave the ocean and enter freshwater to spawn when
winter rains have been sufficient to raise streamflows and, for many coastal
streams, breach the sandbars that form at the mouths during the summer.
Increased streamflow during runoff events appears to provide adults with cues
that stimulate migration and allows improved conditions for fish to pass
obstructions and shallow areas on their way upstream. The season for upstream
migration of CCC steelhead adults lasts from late October through the end of
May, but typically the bulk of migration occurs between mid-December and midApril. The exact timing and rate of migration depend on several factors,
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
4
FISH
Central California Coastal Steelhead (Oncorhynchus mykiss)
including stream discharge, water temperatures, the maturity of the fish, the
behavior of the population, and possibly other factors.
Steelhead have strong swimming and leaping abilities that allow them to ascend
streams, including small tributary streams and headwaters. Steelhead can swim
up to 4.5 feet per second (fps) for extended periods and can achieve burst speeds
of 14 to 26 fps during passage through difficult areas. Leaping ability depends on
the size and condition of fish and hydraulic conditions at the jump.
Given satisfactory conditions, it is conservatively estimated that steelhead can
leap 6 to 9 feet high, though other estimates range from 11 feet (Bell 1986) to as
high as 15 feet (McEwan pers. comm.).
Spawning and Egg Incubation
Steelhead select spawning sites with suitable gravel substrate and sufficient flow
velocity. It is imperative that water circulates through the gravel to provide a
clean (i.e., silt free), well-oxygenated environment for incubating eggs. Adult
steelhead typically select spawning sites where flow velocity is between 1 and
3 fps (Raleigh et al. 1984) and gravel substrates range in size from 0.25 to 4.0
inches in diameter (Bjornn and Reiser 1991). Because nonanadromous rainbow
trout are typically smaller in size than adult steelhead, they often select spawning
sites with smaller spawning gravel (i.e., 0.25 to 2.5 inches in diameter) (Raleigh
et al. 1984).
Typically, sites with preferred features for spawning occur most frequently in the
pool-tail and riffle-head transition areas where water velocity accelerates out of
the pool into the higher-gradient section below and where water upwells from the
gravel substrate. Adult steelhead may also select run habitats that have the right
combination of suitable gravels, velocities, and depths for spawning. In such
areas, the female will create a pit, called a redd, by undulating her tail and body
against the substrate. This process cleans the gravels as it lifts fine sediment into
the current where it is carried downstream. The male fertilizes the eggs as they
are deposited in the redd, and the female covers the eggs with gravel during the
process of digging the next spawning depression immediately upstream. Unlike
all Pacific salmon, which die after spawning, adult steelhead are capable of
returning to the ocean after spawning, typically by June of that same year, and
some survive to spawn again.
The eggs incubate within the gravel and hatch from about 19 to 80 days later at
water temperatures ranging from 60°F to 40°F, respectively (warmer water
temperatures result in shorter incubation times). The average incubation period is
approximately 4–6 weeks. After hatching, the young fish (alevins) remain in the
gravel for an additional 2–6 weeks before emerging from the gravel and taking
up residence in the shallow margins of the stream where they feed primarily on
insects.
Egg incubation and fry emergence success are influenced by several factors,
including water temperature, dissolved oxygen, and the amount of fine sediments
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
5
FISH
Central California Coastal Steelhead (Oncorhynchus mykiss)
(generally less than 3.3 mm) in the substrate. The optimal temperature for
embryo incubation is about 45°F to 54°F (Raleigh et al. 1984). Embryo survival
decreases when the percentage of substrate particles less than 0.25 inches
(6.4 mm) approaches 25% to 30% of substrate volume and is extremely low
when fine sediments volumes are 60% or more (Bjornn and Reiser 1991).
Survival and emergence of fry is generally high when fine sediments are less
than 5% of substrate volume; emergence becomes difficult when the percentage
of fine sediments exceeds 30–40% by volume (Bjornn and Reiser 1991).
Survival of fertilized eggs through hatching and emergence from the gravel can
be limited by substantial changes in flow. For example, high flows and water
velocities during storm events can scour spawning areas and dislodge eggs from
the substrate or cause fine sediments to be deposited on the redds, where it
smothers the eggs or traps emerging fry. Flow reductions during the incubation
period can cause inadequate intragravel water velocity leading to anoxia or high
levels of carbon dioxide. In extremely low flow conditions, the redds can be
completely or almost completely exposed, causing desiccation or high water
temperatures, both of which lead to premature emergence of alevins and high
mortality.
Rearing
After emerging from the gravel, fry inhabit low-velocity areas along the stream
margins. As they feed and grow, they gradually move to deeper and faster water.
In central California streams, juvenile steelhead typically rear in freshwater for
1–3 years before emigrating to the ocean as smolts. While in freshwater, juvenile
steelhead require conditions adequate to sustain growth and survival year-round.
Adequate conditions include streams with the right combination of flow, water
temperature, cover, and food. Steelhead juveniles that are 3–6 inches long, in
their first or second year of life, may be commonly found in riffle habitat,
particularly in warmer streams. Juveniles larger than 6 inches are more often
found in deeper waters where low-velocity areas are in close proximity to higher
velocity areas and cover provided by boulders, undercut banks, logs, or other
objects is available. Generally, heads of pools and deep pockets with riffles are
preferred and defended by larger trout as these areas typically provide easy
access to prey items. In coastal streams, juvenile steelhead inhabit a variety of
habitats in both large and small streams. Often, habitat may be more limiting for
older juveniles than for younger fish, particularly during base flow conditions
that generally occur between May and October in central California. During this
time of year, stream flow often drops to very low levels and results in declining
depths and velocities in riffle and run habitats. In some years and streams, only
isolated pools with intervening dry sections of stream channel may remain during
the summer and early fall. Any diversion or other depletion of stream flow during
this critical period substantially reduces the quantity and quality of habitats can
restrict the distribution of juveniles and reduces the production of the juvenile
population.
Streamflow influences the quantity, quality, and distribution of steelhead rearing
habitat. Stream flow directly affects the amount of available habitat by
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
6
FISH
Central California Coastal Steelhead (Oncorhynchus mykiss)
determining the stream area with appropriate combinations of water depths,
velocities, water temperatures, and streambed characteristics (e.g., substrate
composition, cover) (Orth 1987; Bain et al. 1988).
Ideal steelhead rearing habitat in the late-growing season low-water period is
often characterized by base flows of 50% or more of the average annual daily
flow, summer temperatures of 18°C or less, a pool area of about 40–60% stream
area, stream shading between 50% and 75% of the stream area, abundant food,
and mean depths of one 1 foot or more (Raleigh et al. 1984).
Water temperature is perhaps the most influential controlling factor affecting
juvenile steelhead, particularly during the summer rearing period. In many
central California streams, growth slows or ceases in conjunction with warm,
low-flow conditions that are typical of late summer. The influence of water
temperature on steelhead and other salmonids has been well studied. The
influence of water temperature on individual trout populations is complicated by
a number of factors such as local adaptations, behavioral responses, other habitat
conditions, daily and annual thermal cycles, and food availability. The most
definitive temperature tolerance studies have been conducted in laboratory
settings where experimental conditions have been highly controlled and fish were
exposed to constant temperatures. Based on these studies, the upper incipient
lethal temperature has been determined to range from 24ºC to 25ºC for rainbow
trout. Elevated temperature below the lethal threshold can indirectly influence
survival by depressing growth rate, increasing susceptibility to disease, and
lowering the ability of juveniles to evade predators. Preferred temperatures for
juvenile steelhead range from 12ºC to 18ºC, although optimum growth rates may
occur at slightly higher temperatures if food is abundant (Raleigh et al. 1984).
In most streams, water temperature varies over the course of a day and
seasonally, generally following changes in air temperature and solar radiation.
Although the peak temperature on a given day may exceed the lethal level,
juvenile steelhead can survive short periods at temperatures above the lethal
threshold. For example, Brett (1952) found that juvenile Chinook salmon
experienced no mortality at temperatures up to 24ºC for 7 days. At 26ºC, half the
juvenile salmon survived a 5-hour exposure period, and at 27ºC half survived a
1.5-hour exposure. The temperature that the fish are acclimated to is also an
important variable. Juvenile salmon acclimated to 24ºC experienced 50%
mortality after 8.5 days at 25ºC while those acclimated to 15ºC experienced 50%
mortality after only 42 hours of exposure at 25ºC. During summer, juvenile
steelhead can avoid peak water temperatures by seeking out coldwater refugia (if
available), including tributary streams, deep pools with stratified temperatures,
and areas with upwelling groundwater.
Food and cover also are important factors for rearing steelhead (Mason and
Chapman 1965; Shapovalov and Taft 1954). Availability of food such as aquatic
and terrestrial insects is influenced by substrate composition, and the occurrence
of riffle habitats and riparian vegetation. Generally, the highest production of
aquatic invertebrates occurs in streams with riffle habitats composed of gravel
and cobble substrates containing relatively low amounts of fine sediment. Bjornn
et al. (1977) found that the density of rearing steelhead and Chinook salmon in
artificial channels was reduced in nearly direct proportion to increased cobble
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
7
FISH
Central California Coastal Steelhead (Oncorhynchus mykiss)
embeddedness. The negative response by fish to increased embeddedness was
more pronounced during the winter, presumably because of a reduction in the
availability of over-wintering habitat. During periods of high flow, reduced food
abundance, and lower temperatures occurring in winter, juvenile steelhead often
make use of larger substrate for cover. Backwater habitat, small tributaries, or
other low-velocity areas may also be important winter habitat.
Smith (1999) describes two different habitat types used by CCC steelhead and
resident trout. The primary habitat consists of shaded pools of small, cool, lowflow upstream reaches typical of the original steelhead habitat in the region. In
addition, they can use warm-water habitats below some dams or pipeline outfalls,
where summer releases provide high summer flows and fast-water feeding
habitat. Trout metabolic rate, and thus food demand, increases with temperature.
Trout rely heavily on insect drift for food, and drift increases with flow velocity.
Under conditions of low flow and high temperatures, trout have increasing
difficulty obtaining sufficient food to meet metabolic costs. Smith and Li (1983)
found that in Uvas Creek (Santa Clara County)—a relatively warm stream with
summer maximum water temperature of 23ºC to 25°C—steelhead and/or
rainbow trout move into higher velocity microhabitats in riffles and runs where
sufficient food can be obtained. These habitats are created by summer releases
from an upstream reservoir. Under augmented flow conditions, trout can occupy
warmer habitats than may otherwise be possible, provided that food is abundant.
Smolt Out-Migration
Most juvenile steelhead typically migrate to the ocean from March through June
as stream flow declines and water temperature increases, although some may
migrate downstream in late fall. Before their downstream migration, the juveniles
undergo physiological and morphological changes of smolting that prepare them
for ocean life. Juveniles undergoing the smoltification process experience a wide
range of morphological and behavioral changes, including changes in coloration
(body becoming more silvery, loss of parr marks, and presence of black-tipped
fins), weight-to-length ratio, body shape, and a tendency exhibit schooling
behavior and migrate.
Based on studies on Waddell Creek, smolts migrate downstream as 1- to 4-yearolds, although most do so as 1- and 2-year-olds (Shapovalov and Taft 1954). The
oldest smolts (2- and 3-year-olds) typically emigrate first (March–May) followed
by 1-year-old fish in April–June. Juvenile steelhead typically smolt only after
they have reached a minimum size of about 160 mm (6 inches). In some cases,
growth rate can cause smolts to residualize (i.e., fail to emigrate and revert back
to freshwater residency). Residualization can occur if growth is too quick or too
slow and they do not reach smolting size at the right time of year. Smoltification
occurs in response to increasing photoperiod. Temperature influences the
smoltification process by controlling the rate of the physiological response to
photoperiod; warmer temperatures cause juveniles to smolt more quickly.
However, temperatures in excess of 12ºC have been shown to reduce migratory
behavior and decrease seawater survival in steelhead smolts. Most emigration of
smolts occurs at night, typically in response to lunar phase or freshets.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
8
FISH
Central California Coastal Steelhead (Oncorhynchus mykiss)
During outmigration, smolts are subjected to a variety of environmental and
biological factors that affect their survival. As discussed above, excessive water
temperatures can reduce migratory behavior and decrease seawater survival. In
addition, excessive water temperatures can increase stress, resulting in increased
susceptibility of smolts to disease and predation. Excessively low stream flow
can adversely affect emigration by increasing the travel time of smolts during
their downstream migration or causing stream segments to be impassable if they
become too shallow. In addition to adverse temperature and flow conditions,
predation is another factor that affects the survival of smolts. Smolts are subject
to predation by piscivorous (i.e., fish-eating) birds such as kingfishers,
cormorants, mergansers, herons, terns, and pelicans. Although predation by
piscivorous fish is often a factor in large rivers, large predatory fish are typically
not present in smaller coastal streams. However, introduced warmwater gamefish
species such as largemouth bass, sunfish, and catfish often occur in lower
elevation reaches of coastal streams. Predation can increase under conditions
where smolts have to traverse shallow sections of streams or other areas absent of
cover. Birds can be particularly effective predators when water clarity is high.
Conditions favoring predation by birds occur in channel reaches modified for
flood control or at the head of mainstem reservoirs where the channel is wide and
shallow, and largely devoid of in-stream large woody debris and riparian
vegetation.
Out-Migration of Adults
Steelhead that survive spawning return downstream to reenter the ocean. As
many as 30% of adult spawners may be repeat spawners, and some fish may
return to spawn up to three or four times (Shapovalov and Taft 1954). In some
streams fish return to the ocean immediately after spawning, while in others they
may remain in freshwater for up to several months. After spawning, these fish
typically do not resume feeding while in freshwater. By June, most adults have
returned to the ocean. Fish that remain in the stream for extended periods of time
generally reside in deeper pools. Adequate cover and cool temperature are
important for adults that hold over for the entire summer.
Foraging Requirements
Juvenile steelhead feed primarily on aquatic invertebrates and terrestrial insects.
These fish typically take up position in the stream current and capture drifting
organisms or rise to the surface to take prey items that have fallen into the
stream. Active invertebrates may be taken off the substrate, and occasionally
small fish and snails are eaten. Feeding may occur at any time but often peaks at
dawn and dusk. Trout are primarily visual feeders, so high turbidity can reduce
feeding activity. Feeding activity can also be reduced during winter when
temperature and activity levels are lower.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
9
FISH
Central California Coastal Steelhead (Oncorhynchus mykiss)
Reproduction
CCC steelhead typically mature after 1 or 2 years in the ocean, with males more
commonly maturing in 1 year and females in 2 years. Adult females select
spawning sites with gravel substrates, where water velocities range from 1 to 3.6
fps (frequently 2 fps), and depths range from 0.5 to 3 feet (optimum 1.2 feet)
(Bovee 1978). Generally, larger fish can establish redds and spawn in faster
currents than smaller steelhead (Barnhart 1986). Although gravel substrates are
mostly used, steelhead will also use sand-gravel and gravel-cobble mixtures for
spawning. To keep incubating eggs, well-oxygenated substrates need to be highly
permeable (i.e., relatively free from finer substrates).
Steelhead are relatively highly fecund. A 22-inch female produces around
4,800 eggs, and a 30-inch fish produces an average of 9,000 to 10,000 eggs
(Shapovalov and Taft 1954). By comparison, a 12-inch nonanadromous rainbow
trout may produce 1,000 eggs or more. Spawning of CCC steelhead occurs
primarily from December through March or early April.
Nonanadromous rainbow trout typically mature in their second or third year,
though the range is from 1 to 5 years. Spawning of rainbow trout occurs from
February through June.
Demography
Within anadromous populations there are numerous distinct life-history patterns
involving different combinations of stream rearing seasons, ocean inhabiting
periods, and repeat spawning intervals. Generally, CCC steelhead rear for one to
two years in freshwater and return to spawn after one or two years in the ocean.
Steelhead commonly live for four or five years but rarely can reach seven years
old. The greatest mortality likely occurs during the period immediately following
hatching and into the first summer of growth. Extreme winter storms may also
result in high losses of eggs or fry. Fry production usually greatly exceeds the
rearing capacity of habitat for fish after their first year of growth, and young fish
seeking out unoccupied habitats are often subject to predation. Survival to smolt
stage is generally less than 10%.
Ecological Relationships
In the San Francisco Bay Area, trout are typically found in clear, cool, shaded
stream reaches in the middle or upper reaches of perennial streams in relatively
undisturbed watersheds. In headwater streams the gradient is relatively high,
water is usually clear and saturated with oxygen, streams are well shaded with
relatively cold temperature (seldom exceeding 21°C), and the substrate is
dominated by gravel- and cobble-size classes. Headwater reaches are typically
dominated by rainbow trout, which may be the only fish present. Sculpin,
speckled dace, Sacramento sucker, and California roach may occur with trout in
some areas. The lower extent of trout distribution is regulated by water
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
10
FISH
Central California Coastal Steelhead (Oncorhynchus mykiss)
temperature and the downstream extent of rearing habitats. In coastal streams,
there may be a distinction between a resident trout zone, which occurs above
barriers to migration of anadromous fish, and an anadromous fish zone that
supports migratory steelhead, lamprey, and possibly coho or Chinook salmon
salmon. In some coastal streams the anadromous zone may extend downstream to
reaches with tidal influence.
In freshwater habitats, juvenile steelhead and rainbow trout feed primarily on
small invertebrates. Juveniles, particularly fry are vulnerable to predation by
birds including kingfishers, mergansers, green herons, great blue herons, and
night herons. Garter snakes also prey on juveniles as do raccoons, particularly in
situations where fish are trapped in isolated pools during the dry season.
Population Trend
Global:
Commonly found throughout historic range
State:
Declining
Within HCP Extirpated
Study Area:
Threats and Reasons for Decline
Most San Francisco Bay tributaries historically supported populations of
anadromous steelhead and/or resident rainbow trout, and many still do.
Urbanization, particularly in lower watershed areas, has resulted in habitat
degradation and migration barriers where streams have been modified for flood
control, placed in long underground culverts, bridged, culverted, and
channelized. Urbanization has also altered patterns of streamflow through
increased drainage efficiency, more impervious areas, and in some cases,
increased summer irrigation. Water supply projects have also altered streamflow
through water diversion, storage, and water delivery projects. Dams for water
supply or recreational use have eliminated access to many headwater areas
important to steelhead and rainbow trout. Watershed activities, including
residential development, road construction, farming and livestock grazing, have
resulted in increased delivery of fine sediments and have led to deterioration of
substrate conditions for spawning and food production. Point and non-point
source pollution has degraded water quality with serious consequences for native
fish fauna. Although direct effects of pollution are common (e.g., fish kills),
chronic, nonlethal forms of pollution probably have a more significant effect on
fish populations by reducing growth, reproductive success, and migration of fish,
including steelhead. Increased water diversions by riparian landowners have
reduced summer baseflows in some areas. Unscreened water diversions also
entrain fish, including downstream migrating steelhead juveniles and smolts,
which often leads to mortality of these fish. Expanded human populations have
resulted in increased frequency of contact and likely higher levels of exploitation
through poaching and even legal fishing activities. Climate change, particularly
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
11
FISH
Central California Coastal Steelhead (Oncorhynchus mykiss)
variation in ocean conditions, may result in periods of lower productivity and
reduced survival in the ocean environment for steelhead, particularly in
California where they are near the southern edge of their range. Global increase
in temperature threatens to alter both stream temperature and rainfall patterns
with uncertain consequences.
Within the HCP covered area, direct impacts on steelhead are likely to occur
from water transmission and filtration system operations and maintenance
(O&M) activities. Specific activities expected to have the greatest effect on
covered fish species and their habitats are dam and reservoir operations and
diversion of water for water supply. These activities alter flow parameters such
as the magnitude, frequency, duration, timing, and rate of change. Specifically,
diversions from Alameda Creek to Calaveras Reservoir significantly reduce low
and moderate (i.e., less than 650 cubic feet per second [cfs]) flows in Alameda
Creek downstream of the Alameda Creek Diversion Dam (ACDD) when there is
flow in Alameda Creek. Similarly, the capture of runoff by Calaveras Reservoir
significantly reduces fall, winter, and spring base and peak flows in Alameda and
Calaveras Creeks downstream of Calaveras Dam relative to unimpaired
conditions. These activities could affect flow conditions for covered fish species
that are necessary for adult attraction and migration, spawning, rearing, and
juvenile outmigration. However, dry season (summer) releases, combined with
the cooler water temperatures associated with bottom withdrawals from the
reservoir, could provide improved summer rearing habitat conditions (a benefit)
in Alameda and Calaveras Creeks downstream of Calaveras Reservoir.
In addition to decreases in gravel abundance as a result of reservoir operation,
covered activities would also affect the availability of inundated spawning habitat
for steelhead. Flow reductions occurring during winter (e.g., November–May) as
a result of reservoir operations (specifically, the capture and storage of inflows to
the reservoirs) reduce the area of steelhead spawning habitats below the dams.
This occurs primarily because channel width, water depths and velocities decline
as a function of reduced flow.
Similarly, flow reductions in late fall, winter, and spring would reduce average
and maximum water depths of stream habitats and affect migration of covered
species. Currently, 28 critical riffles have been identified along Alameda Creek
between Stonybrook Creek and Sunol Regional Park (Figure 4-6) (Hanson
Environmental 2002b; Entrix 2004; URS HDR 2010). These critical riffles
potentially impede the upstream migration of steelhead, and possibly Pacific
lamprey and may affect downstream migrating juveniles of these species as well
because of excessively shallow water depths or drying channels. The range of
minimum flows meeting passage criteria for adult steelhead passage at these
identified critical riffles is 1–75 cfs (Hanson Environmental 2002b; Entrix 2004;
URS HDR 2010). Covered activities would reduce the frequency and magnitude
of flows in Alameda Creek that support passage for adult steelhead at these
critical riffles, relative to unimpaired flow conditions (Table 4-11). A recent
analysis of critical riffles in the Sunol Valley quarry reach of Alameda Creek
suggested that non-HCP-related improvements including modification of the
Pacific Gas and Electric (PG&E) concrete apron drop structure and the
installation of cutoff walls to reduce seepage of creek water to adjacent quarry
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
12
FISH
Central California Coastal Steelhead (Oncorhynchus mykiss)
pits may result in channel configuration changes that reduce the amount of flow
needed to pass certain critical riffles (URS HDR 2010).
Other water transmission and filtration system O&M activities with the potential
to affect covered fish include reservoir releases for valve maintenance, rare
discharges from the Sunol Valley Water Treatment Plant, and uncontrolled
reservoir spills. These short-duration spikes in flow cause stream levels to rise
and fall quickly, which can result in redd scour and displacement and/or
stranding of fry and juveniles. However, these activities are expected to occur
relatively infrequently (i.e., occurring only once every year or less) and be of
short duration (i.e., lasting from minutes to days), and impacts are not anticipated
to be high from these activities.
Recreational impacts on steelhead could occur from hiking, biking, and
equestrian use that would be allowed through a permit system and/or guided
tours. Impacts on steelhead would primarily consist of temporary harassment of
individuals through illegal water contact (e.g., wading or entering stream
channels on foot, bicycle, or horseback) by recreationists during spawning or
rearing periods. Overall, recreational use of the watershed would be expected to
remain very low, given that recreational activities will be restricted, and impacts
are not anticipated to be high from this activity.
Indirect impacts on covered fish could occur from activities that affect input of
fine sediment to streams and include both temporary and long-term impacts.
Temporary impacts could occur during bridge replacement and construction, road
construction and maintenance, vegetation management, and other maintenance
and construction activities that result in soil disturbance or loss of vegetative
cover. These activities would result in the disturbance of soil or increased
erosion, which could lead to increased transport and delivery of fine sediments
and pollutants associated with heavy equipment operation to waterways. The
temporal period of disturbance will vary between activities; however, most
activities are anticipated to occur during the summer dry season outside of the
spawning, egg incubation, and migration periods and when the potential for
transporting sediments and pollutants to streams is much lower. Long-term
impacts on steelhead and their habitat associated with increased transport and
delivery of fine sediments to waterways could occur from livestock grazing,
high-traffic livestock areas, vegetation and debris management on dams,
integrated pest management around facilities and roadways, and the addition of
30 miles of unpaved roads in the plan area. The potential magnitude of biological
effects resulting from these activities depends on a number of factors, including
the proximity of the disturbance to the stream, the location of the disturbance
within the watershed (which directly affects the length of stream potentially at
risk), the intensity of the disturbance, soil type (unconsolidated soils are more
easily eroded), and the amount transported to the streams.
The application of fertilizers, as well as pesticides and herbicides associated with
nursery and golf course O&M, could result in the release of small amounts of
polluted runoff to streams. The U.S. Fish and Wildlife Service (USFWS) does
not cover the use of pesticides and herbicides in an HCP but accepts their use as
long as U.S. Environmental Protection Agency (EPA)-established protocols are
followed. DFG does permit coverage of these substances. The potential
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
13
FISH
Central California Coastal Steelhead (Oncorhynchus mykiss)
magnitude of biological effects resulting from the potential introduction of these
contaminants depends on a number of factors, including the proximity to the
stream; the type, amount, concentration and solubility of the contaminant; and
the timing and duration of the discharge. Overall effects of these activities on
steelhead are unknown.
Data Characterization
Historic steelhead presence in the Alameda watershed is documented in relatively
few sources, including photographs, anecdotal accounts, and a few scientific
reports and museum collections. There is little information on relative abundance
of the species or its distribution within the watershed before development of the
watershed. Most of the available information for Alameda Creek is currently
summarized in Gunther et al. (2000) and Leidy et al. (2003).
There is little quantitative information on current population abundance or
abundance trends in the CCC steelhead DPS. The most comprehensive sources
are Titus et al. (in prep) and McEwan and Jackson (1996).
Impassable barriers downstream of potential spawning and rearing habitat areas
currently preclude steelhead from maintaining populations in the upper Alameda
Creek watershed. Planned removal of some of these barriers is expected to result
in steelhead reestablishing populations in the watershed. Resident rainbow trout
populations and adfluvial reservoir populations presumably derived from historic
steelhead populations are currently present in, below, and upstream of existing
reservoirs.
Since 1998, SFPUC has been conducting monitoring on an annual basis of
stream flows, Calaveras Reservoir limnology, Alameda Creek and Calaveras
Creek water quality, and fish population analyses as part of a Memorandum of
Understanding (MOU) with DFG (San Francisco Public Utilities Commission
2007). The monitoring program was expanded in 2002 and 2003 to include
control sites in portions of Alameda Creek upstream of the Alameda Creek
Diversion Dam, La Costa and Indian Creeks upstream of San Antonio Reservoir,
and Arroyo Hondo upstream of Calaveras Reservoir (San Francisco Public
Utilities Commission 2004, 2005a, 2006, 2007). Snorkel, electrofishing, and
spawning surveys have been conducted in both Alameda and Calaveras Creeks
downstream of Calaveras Reservoir, in Arroyo Hondo upstream of Calaveras
Reservoir, and in La Costa and Indian Creeks upstream of San Antonio
Reservoir. In addition, trapping and hook-and-line sampling were conducted in
2003 to estimate the population of adult rainbow trout in Calaveras and San
Antonio Reservoirs (San Francisco Public Utilities Commission 2005b). Based
on these investigations, the adult rainbow trout population in San Antonio
Reservoir was estimated to be 460 fish, while the adult population in Calaveras
Reservoir was estimated to be 304 fish in 2003 (San Francisco Public Utilities
Commission 2005b).
As mentioned above, genetic studies show that rainbow trout currently found in
Calaveras Reservoir are most closely related to trout in upper Alameda Creek and
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
14
FISH
Central California Coastal Steelhead (Oncorhynchus mykiss)
nearby San Antonio Reservoir and are more closely related to coastal steelhead
than to hatchery trout (Nielsen 2003). Although these results are consistent with
the findings of a recent study completed on rainbow trout genetics in neighboring
Santa Clara County (Garza and Pearse 2008), additional genetic studies of
Alameda Creek watershed rainbow trout are likely needed to confirm to what
degree, if any, past trout introductions and current fish stocking practices that
hatchery rainbow trout have affected the genetic integrity of rainbow trout in the
upper Alameda Creek watershed.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
15
HCP Study Area
Central Coast Steelhead ESU
0
100
MILES
FIGURE 1
Central Coast Steelhead (Oncorhynchus mykiss) ESU
Distribution
Source: Adapted from Zeiner et al. 1984.
INVERTEBRATES
Callippe Silverspot Butterfly (Speyeria callippe callippe)
Callippe Silverspot Butterfly
(Speyeria callippe callippe)
Status
State:
None
Federal:
Endangered
Critical Habitat:
Not Designated
Taxonomy
The common names of this butterfly, the callippe silverspot or the callippe
fritillary, are a source of confusion even among entomologists. This is because
both common names actually refer to two taxonomic entities, namely the species
Speyeria callippe, as well as the nominate subspecies Speyeria callippe callippe.
Another source of confusion is the federal Endangered Species Act (ESA), which
from legal and regulatory perspectives refers to both species and subspecies as
“species”. Of the numerous subspecies within this widely distributed species,
only the subspecies S. callippe callippe is protected under federal law.
Like many of the described subspecies of this silverspot species, Speyeria
callippe callippe exhibits considerable phenotypic variation in its color, wing
markings (maculations), and the amount of black scaling. Individuals of
S. callippe callippe exhibit the following features:

dorsal forewings with thick, dark veins in males and prominent black
maculations;

dorsal wings with pale yellow-orange ground color with an extensive black,
sooty-appearing suffusion in the basal area of the forewings and hindwings;

ventral forewings with extensive reddish color in males; and

ventral hindwings with a brown disc covered with yellow suffusion.
A closely related subspecies, S. callippe comstocki, differs from typical S.
callippe callippe by exhibiting a reduced basal suffusion of black, sootyappearing scales on the dorsal wings, mostly yellow color on the ventral
forewings of males, and a mostly yellow disc. A couple of related subspecies
lack the silverspots that give this species its common name.
Both subspecies of Speyeria callippe (i.e., callippe callippe and callippe
comstocki) are known to occur in the greater San Francisco Bay area. Individuals
with more black sooty scaling in the basal portions of the forewings and
hindwings, reddish ground color on the forewings, and browner discs, occur in
populations located closer to the coast, where the black scales and darker wing
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
1
INVERTEBRATES
Callippe Silverspot Butterfly (Speyeria callippe callippe)
colors probably aid this cold-blooded butterfly in absorbing radiant energy from
the sun. Inland populations, where temperatures are warmer and there is less fog,
exhibit less black scaling and sootiness, plus lighter, yellowish wing colors.
Due to the high degree of variation exhibited by individuals within a particular
population, as well as geographic variation among populations, the limits of the
variation have not been well defined and correlated with the subspecific
taxonomic categories. As a result, it is often difficult to identify individual
specimens and even populations to the subspecific level without examining a
long series of specimens to determine which characteristics are prevalent in a
particular population. Even then, some populations tend to exhibit more
intermediate characteristics. Since wing colors and maculations may fade with
age and scales are lost with age, this further complicates making taxonomic
decisions at the subspecific level.
Range
The callippe silverspot (Speyeria callippe callippe) is endemic to the San
Francisco Bay area and core populations are in the San Bruno Mountain in San
Mateo County and the Joaquin Miller Park. Historically, populations occurred on
the west side of San Francisco Bay from Twin Peaks in San Francisco to the
vicinity of La Honda in San Mateo County. In the East Bay, populations were
known from northwestern Contra Costa County southward to the Castro Valley
area of Alameda County (Howe 1975; BUGGY Data Base 2004) (Figure 1).
The butterfly in the watershed is known as "near" Speyeria callippe callippe
displaying intermediary characteristics between S. calippe callippe and
S. callippe comstocki (not endangered). Additional populations of the species
S. callippe occur in the Sky Valley-Lake Herman area of southern Solano County
and in the north central and northeastern portions of Alameda County (Arnold
1981; Murphy and Weiss 1990). Because the species populations are similar in
appearance to the endangered subspecies, the U.S. Fish and Wildlife Service
(USFWS) has recommended that other project proponents in these areas treat
these populations as the endangered subspecies.
Occurrences within the HCP Study Area
There is one historical record for the callippe silverspot butterfly from a nonspecific location along Calaveras Creek. The specimens were collected in 1903
and are housed at the California Academy of Sciences in San Francisco (BUGGY
Data Base 2004). There are no occurrences records for this subspecies in the
California Natural Diversity Database (CNDDB) (California Natural Diversity
Database 2008).
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
2
INVERTEBRATES
Callippe Silverspot Butterfly (Speyeria callippe callippe)
Biology
Habitat
The callippe silverspot occurs in grasslands where its sole larval food plant,
johnny jump-up or violet (Viola pedunculata) (Violaceae), grows. It has been
observed in grazed and ungrazed grasslands. The silverspot occurs in hilly terrain
with a mixture of topographic relief. Adults will visit the margins of oak
woodlands and riparian areas in search of nectar, as well as disturbed areas if
favored nectar plants grow there. The three primary habitat requirements of the
callippe silverspot are:

grasslands supporting its larval food plants;

hilltops for mate location; and

nectar plants in the grasslands or nearby oak woodlands, riparian areas, or
disturbed areas.
Because the butterfly has been observed flying distances of approximately one
mile (Arnold personal observation; Thomas Reid Associates 1981), these three
habitat features do not necessarily have to coincide.
Breeding Habitat Requirements
The larval food plant is Viola pedunculata. Although this food plant is a
perennial, the above ground growth dies back annually. It is often associated with
soils characterized by clay deposits in grazed and ungrazed grasslands of the San
Francisco Bay Area.
The sequence of life history events for the callippe silverspot can be described as
follows. The butterfly has one generation per year (univoltine). There are four
stages in the butterfly’s life cycle: egg, larva (i.e., caterpillar), pupa, and adult.
Upon hatching from the egg, newly emerged larvae search for a suitable hiding
place such as under a rock, where they enter a physiological resting stage,
referred to as diapause. Many of the young die during this stage. During the
following rainy season, larvae begin feeding on the food plant once it sprouts
new foliage, typically in late January or early February. They continue to feed as
weather conditions allow them to be active during the next four months. Then
they pupate and transform into the adult silverspot.
The adult flight season is about six to eight weeks in length, starting in mid-May
and terminating in mid-July. Actual starting and ending times can vary by a few
weeks from year-to-year and in different locations within the same year. Results
of a capture-recapture study indicate that average adult life span is about 5–
7 days, but individuals have lived in the lab for as long as 10–14 days (Arnold
1981).
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
3
INVERTEBRATES
Callippe Silverspot Butterfly (Speyeria callippe callippe)
Foraging Requirements
Because of the length of the flight season, adults forage on flowers of several
different plant species to obtain nectar as these plants flower during different
periods of the flight season. When available, the adult silverspot feed on nectar
plants including mints, especially Monardella, and thistles, such as Silybum,
Carduus, and Cirsium, and buckeyes (Aesculus) (Arnold 1981). Foraging may
occur at flowers of numerous other plant species depending upon their
availability at a particular location. Areas where the larval and adult food plants
grow do not always coincide with areas where mate location and other behaviors
occur. The aforementioned thistles often grow in quite disturbed portions of the
silverspot’s habitat.
Demography
Although monitoring of the silverspot population has occurred at San Bruno
Mountain since 1980, the methods used have not been consistent during this
period to identify an actual population trend. Nonetheless, annual population
numbers are likely influenced by seasonal weather patterns (i.e., density
independent), but moisture from the fog drip may somewhat ameliorate weather
factors (Arnold 1981).
Dispersal
Because the leaves of Viola pedunculata are typically dry by the start of the adult
flight season, females frequently lay their eggs in or near areas where Viola
grows. For this reason, newly hatched larvae of the callippe silverspot do not
feed before they find a suitable diapause location. When Viola sprouts during the
following winter, the larvae have to search for the food plant. Also, developing
larvae usually feed at night, but crawl off of the food plant and hide nearby
during the daytime. Thus, short distance dispersal, probably on the order of tens
of feet, occurs routinely during the larval stage.
During a capture-recapture study on San Bruno Mountain, approximately 5% of
recaptured adults moved between 4,800 and 7,400 feet (Thomas Reid Associates
1981). While tracking adult silverspots, Arnold (personal observation) observed
them flying distances of about one mile to nectar at Aesculus blossoms.
Behavior
Adults tend to congregate on prominent hilltops, a behavior known as
hilltopping, where they search for potential mates. Adult males also incessantly
patrol their breeding habitat in search of newly emerged females, while females
tend to spend more time in non-flight activities than males. For example, field
observations revealed a higher percentage of basking, perching, and foraging
behavior by females compared to males (Arnold 1981).
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
4
INVERTEBRATES
Callippe Silverspot Butterfly (Speyeria callippe callippe)
Ecological Relationships
Although not documented, sun exposure, topographic aspect, and microclimatic
conditions at ground level probably affect the developmental rates of immature
stages and the seasonal activity of adult silverspots. The dark scaling on the
wings that is characteristic of the endangered subspecies is observed more
frequently at locations within the fog belt. Since the silverspot is cold-blooded
and dependent upon solar radiation and ambient air temperature to maintain its
activity, the darker coloration of adult butterflies at locations that experience
foggier conditions is undoubtedly an adaptation to warm up in an environment
that can be inhospitable to other butterflies.
Data Characterization
There is limited recent information about this subspecies. Extensive surveys were
conducted to quantify suitable habitat for butterflies in the HCP area (Arnold
2004). These surveys found that within the plan area, callippe silverspot butterfly
could occur in grasslands, including hilly terrain with a mixture of topographic
relief. Adults visit the margins of oak woodlands and riparian areas in search of
nectar, as well as disturbed areas if favored nectar plants grow there. A recovery
plan is being prepared by USFWS for the callippe silverspot, but is not available
at this time. Critical habitat has not yet been designated for the butterfly.
Population Trend
Global:
Unknown
State:
Declining
Within HCP Unknown
Study Area:
Threats
Loss and alteration of habitat, primarily through urbanization and habitat
degradation by non-native plants, are some of the factors contributing to the
decline of the callippe silverspot. Overgrazing can be detrimental, but properly
managed grazing can enhance callippe silverspot’s grassland habitat by
preventing other plant species from outcompeting the butterfly’s host plant (U.S.
Fish and Wildlife Service 1997). Increased frequency of fire may also be
detrimental, but this impact would require further study. The population at
Joaquin Miller Park-Redwood Regional Park in Oakland (Alameda County) may
have gone extinct as no adults have been seen there for approximately 20 years.
Because of its shrinking geographic range and threats from poaching, USFWS
(1997) recognized the callippe silverspot from the two aforementioned localities
as an endangered species. The USFWS has also recognized dust from quarrying
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
5
INVERTEBRATES
Callippe Silverspot Butterfly (Speyeria callippe callippe)
operations as a potential threat to the species, because abundant dust could clog
the spiracles of larvae and adults, interfering with their respiration (U.S. Fish and
Wildlife Service 1997). Callippe silverspot butterflies are also very sensitive to
pesticide use.
Direct impacts on callippe silverspot butterfly habitat in the HCP study area
could occur from watershed operations and maintenance (O&M),
lease/permitting, and easement activities and some water transmission and
filtration system O&M. The specific activities expected to have the greatest
effect on suitable butterfly habitat are road construction and vegetation
management in nonnative grasslands. Other activities with lesser impacts hightraffic livestock areas, fence installation, replacement and repair of bridges,
fences and gates, road maintenance, boat launch construction, and maintenance
of telecommunication sites. These activities could remove habitat or affect it
temporarily.
Removal of habitat would occur when new roads, bridges, and other features are
constructed. Because the watershed area is a relatively low-use area for the
species, the operation of new facilities such as roads and bridges (e.g., vehicular
traffic) is not expected to extensively disrupt butterfly use of adjacent habitat.
Other direct impacts would consist of permanent impacts on habitat through
construction of new trails, staging areas, and parking/restroom facilities. Overall
recreational use of the watershed would be expected to remain relatively low.
Impacts from high-traffic livestock areas would include trampling, soil
compaction, and temporary removal of vegetation. Impacts from these activities
on callippe silverspot butterfly habitat are expected to be temporary.
Additional temporary impacts could include roadside maintenance, which occurs
once a year or less, consisting of a brief mowing of a 4-foot strip along the road.
These areas are expected to recover after mowing. Bridge- and road-construction
activities could include road grading or construction of armored creek crossings
at ephemeral or intermittent streams. During bridge or road construction,
temporarily disturbed areas (e.g., staging areas) would be used for a longer
duration, but after construction is over, the area would be returned to its original
condition, including revegetation with larval host present if previously present.
Indirect impacts on the butterfly could include increased dust from vehicle
traffic, livestock, and human disturbance that could reduce growing conditions
for host plants (Viola pedunculata). Livestock grazing will also have notable
benefits to the species by reducing competition of host plants with non-native
annual plants, depending on the timing of grazing). Invasive weed control
proposed in the conservation strategy should limit or reduce the spread of
invasive plants, but covered activities may cause weeds to spread in specific
instances. Fire suppression and/or burning could affect butterfly habitat if
conditions are made more suitable for non-native species as a result of the fire.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
6
YOLO
SOLANO
NAPA
SACRAMENTO
SONOMA
SAN JOAQUIN
MARIN
San
Pablo
Bay
CONTRA COSTA
Pacific
Ocean
Alcatraz
Island
SAN
FRANCISCO
San
Francisco
Bay
ALAMEDA
HCP Study Area
Known Population Locations
SAN MATEO
0
10
MILES
FIGURE 1
Callippe Silverspot Butterfly (Speyeria callippe callippe)
Distribution
Source: Jones & Stokes
SANTA CLARA
MAMMALS
Townsend’s Western Big-Eared Bat (Corynorhinus townsendii townsendii)
Townsend’s Western Big-Eared Bat
(Corynorhinus townsendii townsendii)
Status
State:
Species of Special Concern
Federal:
None
Other:
Western Bat Working Group High Priority Species
Critical Habitat:
N/A
Range
Townsend’s western big-eared bats (Corynorhinus townsendii townsendii) occur
throughout most of western North America from British Columbia to central
Mexico, east to the Black Hills of South Dakota, and across Texas to the
Edwards Plateau (Hall 1981; Kunz and Martin 1982). Isolated, relictual
populations of this species are found in the southern Great Plains and the Ozark
and Appalachian Mountains (Hall 1981; Kunz and Martin 1982). The subspecies
pallescens occurs in Washington, Oregon, California, Nevada, Idaho, Arizona,
Colorado, New Mexico, Texas, and Wyoming. The subspecies townsendii occurs
in Washington, Oregon, California, Nevada, Idaho, and possibly southwestern
Montana and northwestern Utah (Handley 1959; Hall 1981). In California, the
boundary between pallescens and townsendii runs north–south approximately
through the center of the Central Valley, with C. t. townsendii on the west side
(Hall 1981). This species occurs from near sea level to well above 3,160 meters
above sea level (Pearson et al. 1952; Nagorsen and Brigham 1993).
Occurrences within the HCP Study Area
Townsend’s big-eared bat is found throughout the western portion of California
(Figure 1), but specific details on its distribution within the central Coast Ranges
are not well known. Records of this species include sites in the coastal lowlands
and agricultural areas of Alameda, Marin, Napa, and San Mateo counties and
nearby hills (Pierson 1988). There is one occurrence record of this species from
within the HCP study area (California Natural Diversity Database 2008).
However, foraging habitat and some suitable breeding habitat occurs in the study
area in buildings, bridges, caves, and cliff crevices.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
1
MAMMALS
Townsend’s Western Big-Eared Bat (Corynorhinus townsendii townsendii)
Biology
Habitat
Townsend’s big-eared bats can occur in a variety of habitats throughout
California, but they are most commonly associated with desert scrub, mixed
conifer forest, and piñon-juniper or pine forest habitat. Within these
communities, they are specifically associated with limestone caves, mines, lava
tubes, and buildings (Dalquest, 1947, 1948; Graham 1966; Pearson et al. 1952;
Kunz and Martin 1982; Pierson et al. 1991; Dobkin et al. 1995).
During hibernation, Townsend’s big-eared bats typically prefer habitats with
relatively cold (but above freezing) temperatures in quiet, undisturbed places.
These areas are often in the more interior, thermally stable portions of caves and
mines (Barbour and Davis 1969; Dalquest 1947; Humphrey and Kunz 1976;
Pearson et al. 1952; Zeiner et al. 1990). Hibernating bats are also often found in
ceiling pockets (Pierson et al. 1991). In central California, solitary males and
small clusters of females are also known to hibernate in buildings (Pearson et al.
1952; Kunz and Martin 1982). Females may roost in colder places than males
during these periods (Pearson et al. 1952).
During spring and summer, females establish maternity colonies in the warm
parts of caves, mines, and buildings (Dalquest 1948; Pearson et al. 1952; Twente
1955; Pierson et al. 1991). In California, some maternity roosts may reach 30ºC
(86ºF) (Pierson et al. 1991). Favored roost locations for females and young are
often in a ceiling pocket or along the walls just inside the roost entrance (Pierson
et al. 1991). Night roosts may include buildings or other structures such as
bridges (Pierson et al. 1996).
Foraging Requirements
Townsend’s big eared bats feed primarily on small moths but take other insects,
including flies, lacewings, dung beetles, and sawflies (Whitaker et al. 1977; Kunz
and Martin 1982). In northern California, studies using radio tracking have found
Townsend’s big-eared bats foraging within forested habitats and along heavily
vegetated stream corridors, avoiding open, grazed pasture land (Pierson and
Fellers 1998; Pierson et al. 1999). Individuals may travel up to 13 kilometers
from their day roost (Pierson et al. 1999).
Reproduction
Female Townsend’s big-eared bats arrive at maternity roost sites in early spring
and give birth to a single offspring in late spring or early summer after an
approximately three-month gestation period (Pearson et al. 1952). In California,
young are born over a three- to five-week period beginning in late May.
Maternity colonies disperse in fall, and mating occurs in fall and winter. The
peak of copulations occurs from November through February, although some
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
2
MAMMALS
Townsend’s Western Big-Eared Bat (Corynorhinus townsendii townsendii)
females apparently mate before arriving at hibernacula (Kunz and Martin 1982).
Females are sexually mature and mate by their first autumn. However, as in most
bats, females store sperm, and ovulation does not occur until early spring
(Pearson et al. 1952). Ovulation may occur either before or after females leave
hibernation. Townsend’s big-eared bats are large at birth, weighing
approximately 25% of the mother’s postpartum mass (Kunz and Martin 1982).
Young grow rapidly, reaching adult size in approximately one month, and
capable of flight in two-and-a-half to three weeks. They are fully weaned by six
weeks (Pearson et al. 1952).
Demography
Band recoveries show longevity records of up to 16 years, five months (Paradiso
and Greenhall 1967) and 21 years, two months (Perkins 1994). Pearson et al.
(1952) estimated the annual survivorship for Townsend’s big-eared bats was
about 50% for young and 80% for adults.
Behavior
Townsend’s big-eared bat is a relatively sedentary species for which no longdistance migrations have been documented (Pearson et al. 1952; Barbour and
Davis 1969; Humphrey and Kunz 1976). The longest seasonal movements
recorded for this species are 32.2 kilometers in California (Pearson et al. 1952)
and 39.7 kilometers in Kansas (Humphrey and Kunz 1976).
Townsend’s big-eared bats hibernate in mixed-sex aggregations of 100 to
500 individuals. They periodically arouse during winter and move to alternate
roosts. Individuals actively forage and drink throughout winter (Brown et al.
1994). Hibernation is prolonged in colder areas and intermittent where climate is
predominately not freezing (Kunz and Martin 1982).
Ecological Relationships
Townsend’s big-eared bat is a lepidopteran specialist; over 90% of the bat’s diet
consists of moths (Pierson et al. 1999). Night roosts of this species often include
other bat species, including pallid bat (Antrozous pallidus), big brown bat
(Eptesicus fuscus), California myotis (Myotis californicus), small-footed myotis
(M. ciliolabrum), long-eared myotis (M. evotis), little brown bat (M. lucifugus),
fringed bat (M. thysanodes), long-legged bat (M. volans), and Yuma myotis
(M. yumanensis).
Population Trend
Global:
Declining (Pierson et al. 1999)
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
3
MAMMALS
Townsend’s Western Big-Eared Bat (Corynorhinus townsendii townsendii)
State:
Declining (Pierson 1988, Pierson and Rainey 1996)
Within HCP Unknown
Study Area:
Threats
Townsend’s big-eared bats are highly sensitive to roost disturbance. Activities
that can result in significant disturbance or loss of habitat include mine
reclamation, renewed mining, water impoundments, recreational caving, loss of
building roosts, and bridge replacement (Kunz and Martin 1982; Pierson et al.
1999). Pesticide contamination may also threaten this species in agricultural
areas (Geluso et al. 1976).
Within the HCP area, repair or reconstruction of abandoned structures and/or
bridges have the potential to affect night-roosting bats or day-roosting bachelors.
The primary covered activity that could affect this species is recreation which has
the potential to disturb roosting bats. Indirect impacts on Townsend’s western
big-eared bat include increased noise and human disturbance. Recreation could
lead to increased harassment or disturbance, even though limitations on
recreation will likely avoid human impacts.
Data Characterization
A moderate amount of literature is available for the Townsend’s western bigeared bat because of its rare and declining status. Most of the information
available is on the natural history, distribution, population status, and threats to
this species. A conservation assessment and conservation strategy has been
published.
Species Distribution in HCP Study Area
Core habitat for the western big-eared bat is defined as habitat primarily used for
maternity roosts. Suitable habitat for maternity roosts can be found within the
HCP study area in urban developed habitats and rock outcrops where caves,
tunnels, mines, and buildings provide protection from the elements and predators
and provide the correct thermal environment for reproduction. Maternity roost
sites are warmer and more consistent in temperature because breeding females
need to maintain a high metabolism to aid in lactation and juvenile bats need to
keep warm to maintain a metabolic rate that allows for rapid growth.
Other habitat is defined as habitat not primarily used for breeding, but used for
other components of the species’ life history such as dispersal and movement,
hibernation, and foraging. Day roosts are areas where bats spend the non-active
period of the day resting or in torpor, depending on the weather conditions. Day
roosts provide shelter from the elements and safety from predators. Night roosts
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
4
MAMMALS
Townsend’s Western Big-Eared Bat (Corynorhinus townsendii townsendii)
are used by bats to rest between foraging bouts, to allow for digestion of prey, to
escape from predators, and to provide shelter from weather. Night roosts are
typically sites that retain heat from the day to aid the bats in maintaining the
higher metabolism necessary for digestion. Winter roosts are areas that have a
stable low temperature suitable for hibernating or prolonged periods of torpor. In
addition to urban developed and rock outcrops habitats, Diablan sage scrub, oak
woodland, riparian woodland, evergreen oak woodland, serpentine pine
woodland chaparral are considered suitable habitats for day, night and winter
roosts.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
5
Species Range
HCP Study Area
Breeding Range
0
100
MILES
FIGURE 1
Townsend's Big-Eared Bat (Corynorhinus townsendii towsendii)
Distribution
Source: Adapted from Zeiner et al. 1990b.
PLANTS
Round-Leaved Filaree (Erodium macrophyllum)
Round-Leaved Filaree (California macrophylla)
Status
Federal:
None
State:
None
California Native
Plant Society:
List 1B.1
Range
Round-leaved filaree (California macrophylla) ranges from northern California,
south into northern Mexico, and east to southern Utah (Taylor 1993). In
California, it is known from scattered occurrences in the Central Valley, southern
North Coast Ranges, San Francisco Bay Area, South Coast Ranges, Channel
Islands, Transverse Ranges, and Peninsular Ranges (Taylor 1993; California
Natural Diversity Database 2008) (Figure 1). It most often occurs in foothill
locations at elevations between 200 and 2,000 feet, but it has been collected from
locations as low as 30 feet and as high as 4,000 feet.
Occurrences within the HCP Study Area
No occurrences of round-leaved filaree have been reported from the HCP study
area. The closest known occurrence to the HCP study area is approximately nine
miles to the east, at Corral Hollow (California Natural Diversity Database 2008).
ICF Jones & Stokes did not survey for this species during the 2003 survey.
Biology
Physical Description
Round-leaved filaree is an annual herb in the geranium family (Geraniaceae).
The plants are small and low growing. The blooming period is from March to
May (California Native Plant Society 2008).
Habitat
Very little is known about the ecological requirements of round-leaved filaree. It
generally occurs in valley and foothill grassland or cismontane woodlands
(California Native Plant Society 2008). California Natural Diversity
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
1
PLANTS
Round-Leaved Filaree (Erodium macrophyllum)
Database(CNDDB) occurrence records indicate that round-leaved filaree is found
most commonly in grasslands on clay soils (California Natural Diversity
Database 2008). It has been found in nonnative grassland on north- or east-facing
slopes on clay soils with relatively low cover of annual grasses (Jones & Stokes
2002, 2003). It most often occurs in foothill locations at elevations between 200
and 2,000 feet, but it has been collected from locations as low as 30 feet and as
high as 4,000 feet (California Natural Diversity Database 2008). Habitat for
round-leaved filaree is potentially present in the HCP study area in nonnative
grasslands. Table 1 shows other species associated with round-leaved filaree.
Table 1. Species Associated with Round-Leaved Filaree
Taxonomic name
Common Name
Triteleia laxa
Ithuriel’s spear
Achyrachaena mollis
blow-wives
Amsinckia lycopsoides
tarweed fiddleneck
Plagiobothrys acanthocarpus
adobe popcorn-flower
Lepidium nitidum
shining peppergrass
Lotus wrangelianus
Chile lotus
Convolvulus simulans
small-flowered morning-glory
Lupinus succulentus
arroyo lupine
Apiastrum angustifolium
wild celery
Madia radiata
showy tarweed
Hemizonia halliana
Hall’s tarweed
Thelypodium lemmonii
Lemmon’s thelypodium
Population Trend
Global:
Unknown
State:
Unknown
Within HCP Unknown
Study Area:
Threats
Round-leaved filaree is known from only a limited number of occurrences and
may be endangered throughout its range (California Native Plant Society 2008).
Population trends are generally unknown because most populations have not
been observed recently (California Natural Diversity Database 2008). Reiser
(1994) reports that populations in southern California are declining due to habitat
loss. Threats may include disturbance from recreational activities, grazing, illegal
dumping, and erosion (California Natural Diversity Database 2008).
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
2
PLANTS
Round-Leaved Filaree (Erodium macrophyllum)
Permanent loss of habitat for round-leaved filaree could result from bridge
replacement and construction, and possibly from high-traffic livestock use. Other
covered activities would have only temporary impacts on plant habitat and plant
populations. Indirect impacts on round-leaved filaree from Plan implementation
could include increased dust, livestock and human disturbance, spread of
nonnative invasive species, change in fire regime, and changes to surface
hydrology. Overall, however, implementation of the HCP is expected to have a
net benefit on the round-leaved filaree because of the improved habitat and
population management.
Special Biological Considerations
The observation of round-leaved filaree on fire trails suggests that disturbance
that opens up vegetation gaps may provide a benefit to the populations (Jones &
Stokes 2002, 2003). The nature of this benefit is not clear, but could range from
uncovering buried, dormant seeds to providing a micro-site free from competing
nonnative grasses. If this speculation is correct, then management actions that
imitate disturbance may help to restore or enhance existing populations.
Data Characterization
The location database for round-leaved filaree includes 93 data records from
1862 to 2006 (California Natural Diversity Database 2008). All but three of the
occurrences are presumed to be extant.
Very little information is available for round-leaved filaree. The literature on the
species pertains primarily to its taxonomy. The main sources of general
information on this species are the Jepson Manual (Hickman 1993) and the
California Native Plant Society (California Native Plant Society 2008). Specific
observations on habitat and plant associates, threats, and other factors are present
in the CNDDB (California Natural Diversity Database 2008).
Modeled Species Distribution in HCP Study Area
Model Description
Model Assumptions
1. Primary habitat: Non-native grassland between 200 and 2,000 feet on northand east-facing slopes on clay or clay loam soils.
2. Secondary habitat: All other non-native grassland below 4,000 feet on northand east-facing slopes.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
3
PLANTS
Round-Leaved Filaree (Erodium macrophyllum)
Model Rationale
The CNDDB records indicate that round-leaved filaree generally occurs in
grasslands on clay soils (California Natural Diversity Database 2008). It has been
found in non-native grassland on north- or east-facing slopes on clay soils with
relatively low cover of annual grasses (Jones & Stokes 2002, 2003). It most often
occurs in foothill locations at elevations between 200 and 2,000 feet, but it has
been collected from locations as low as 30 feet and as high as 4,000 feet
(California Natural Diversity Database 2003). For the purpose of the model, clay
or clay loam soils were defined as those soils described in the Alameda and Santa
Clara soil surveys as having a clay or clay loam component in the upper
16 inches of the soil profile (Welch et al. 1966; Lindsey 1974).
Model Results
According to the model, 129 acres of round-leaved filaree primary habitat and
112 acres of secondary habitat are found in the study area (Figure 2). The
primary habitat is found principally on the hillslopes surrounding San Antonio
Reservoir. A significant area of primary habitat also occurs to the southwest of
Calaveras Reservoir, with smaller areas at the confluence of Alameda and
Leyden Creeks, at the eastern end of Niles Canyon, and in the western part of the
Sunol Valley. Secondary habitat for round-leaved filaree is primarily found along
Oak Ridge, Apperson Ridge and parallel ridges to the northeast.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
4
HCP Study Area
Species Range
0
100
MILES
FIGURE 1
Round-leaved filaree (Erodium macrophyllum)
Distribution
Source: CNDDB 2003
Figure 2 Habitat Distribution Model for Round-leaved Filaree (Erodium macrophylllum)
Legend
guna
o de l a L a
r oy
I-6
Ar
ou
te
80
84
o
s R
ecito
ad
Primary Habitat
oa
Sunol
d
th
Seconary Habitat
Fo
R
R
i ll
Val lecito '
sC
Al a
m
ree
ke
La
Ni
le
s
C anyon
o
d
V all
/ R
k
ed
a
eek
Re
s
Sa
De
l
n A
C
ni
o
Sa n
to
An
re
ek
W
ill
ia
m
s
G
Stream
u
lc
Primary Road
Reservoir
Secondary Road
Study Area
h
La
st
Co
County Line
aC
id
Sh er
e
o
k
ee
rs
Cr
Cre e k
p
n
s
p
dia
In
ad
yne
Ha
h
Gulc
We
lc h
SFPUC Ownership
k
Ro
A
re e
an
Fremont
Va
lle
io
on
80
-6
ir
vo
nt
d
s Roa
alavera
C
y
lle
Va
nol
I
Su
er
Cr
n
R
©
id
g
e
L
de
ey
n
Cr
ee
k
A lam e
d a Cr
ee
k
Oa
Ca
la
We
0
I - 68
lle r
0
I-88
ve
R o ad
Re
se
rvo
e
0
Santa Clara Co.
ir
o
rt
Ho
e
o
v
ro y
Ar
P
y
R
r sh
d
oa
Ma
Alameda Co.
dg
0.5
1
1:100,000
as R o a d
o ad
er R
Fe lt
Ri
ra s
C al a ver
Milpitas
k
nd
o
R
id
g
Calav
er
e
as
e
Cre
k
Mt.
Day
2
Miles
PLANTS
Fragrant Fritillary (Fritillaria liliacea)
Fragrant Fritillary (Fritillaria liliacea)
Status
Federal:
None
State:
None
California Native
Plant Society:
List 1B.2
Range
Fragrant fritillary (Fritillaria liliacea), a member of the lily family (Liliaceae), is
known from 59 occurrences (California Natural Diversity Database 2008). It is
endemic to central western California, ranging from Sonoma and Solano
Counties south to Monterey County (Ness 1993) (Figure 1).
Occurrences within the HCP Study Area
No occurrences of fragrant fritillary have been reported from the HCP study area.
Two occurrences are known from about 14 miles northwest of the HCP study
area, in San Leandro (California Natural Diversity Database 2008). Another
historic occurrence was known from Alum Rock Park, 2.6 miles south of the
HCP study area (California Natural Diversity Database 2008). ICF Jones &
Stokes did not survey for this species in 2003.
Biology
Physical Description
Fragrant fritillary is an herbaceous perennial that produces a bulb. Baranova
(1981) found variation in the structure of this bulb depending on growth
conditions. The plants grow to 12–15 inches tall, producing 2–20 leaves (Ness
1993). Fragrant fritillary blooms from February to April (California Native Plant
Society 2008), each plant producing one to several white flowers.
Habitat
Fragrant fritillary occurs in grasslands and coastal scrub, often on serpentinite,
from sea level to 1,345 feet elevation (California Natural Diversity Database
2008). Serpentine grasslands in the HCP study area are potential habitat for this
species. Table 1 shows species associated with fragrant fritillary.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
1
PLANTS
Fragrant Fritillary (Fritillaria liliacea)
Table 1. Species Associated with Fragrant Fritillary
Taxonomic name
Common Name
Nassella pulchra
purple needlegrass
Dichelostemma pulchellum
blue dicks
Chlorogalum pomeridianum
soaproot
Zigadenus fremontii
Fremont’s star-lily
Camissonia ovata
sun-cups
Fritillaria affinis
checker lily
Baccharis pilularis
coyote brush
Population Trend
Global:
G2 (6-20 element occurrences (EOs) OR 1,000–3,000
individuals OR 2,000–10,000 acres)
State:
S2.2 (6-20 EOs OR 1,000–3,000 individuals OR 2,000–10,000
acres; threatened)
Within HCP Unknown
Study Area:
Threats
Eleven fragrant fritillary occurrences are believed to be extirpated (California
Natural Diversity Database 2008). Two populations are reported as stable and a
third is reported as decreasing, but population trends for the other occurrences are
unknown (California Natural Diversity Database 2008). For 21 occurrences, the
habitat in which fragrant fritillary occurs is rated good to excellent, suggesting
that the populations are likely to be stable. Habitat quality is rated as fair for five
occurrences and unknown for 17 occurrences. Grazing by sheep and cattle and
rooting for bulbs by feral pigs appear to be the most widespread threat to
occurrences (California Natural Diversity Database 2008). Other threats appear
to be localized and include competition from invasive exotic species; road
maintenance and roadside management; recreation activities such as trail use and
maintenance, trampling, and collecting; residential and recreational
developments; landscaping runoff; and natural events such as erosion and land
slides (California Natural Diversity Database 2008).
Permanent loss of habitat for fragrant fritillary could result from bridge
replacement and construction, and possibly from high-traffic livestock use. Other
covered activities would have only temporary impacts on plant habitat and plant
populations. Indirect impacts on round-leaved filaree from Plan implementation
could include increased dust, livestock and human disturbance, spread of
nonnative invasive species, change in fire regime, and changes to surface
hydrology.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
2
PLANTS
Fragrant Fritillary (Fritillaria liliacea)
Data Characterization
The location database for fragrant fritillary includes 59 data records from 1875 to
2004 (California Natural Diversity Database 2008). Seventeen occurrences were
documented in the previous 10 years. Thirty-five of the occurrences are of high
precision and may be accurately located.
Very little information is available for fragrant fritillary. The literature on the
species pertains primarily to its taxonomy. The main sources of general
information on this species are the Jepson Manual (Hickman 1993) and the
California Native Plant Society (California Native Plant Society 2008). Specific
observations on habitat and plant associates, threats, and other factors are present
in the California Natural Diversity Data Base (California Natural Diversity
Database 2008).
Modeled Species Distribution in HCP Study Area
Model Description
Model Assumptions
1. Primary habitat: Serpentine grassland below 1,345 feet.
2. Secondary habitat: Serpentine grassland above 1,345 feet.
Model Rationale
Fragrant fritillary occurs in grasslands and coastal scrub, often on serpentinite,
from sea level to 1,345 feet elevation (California Natural Diversity Database
2008). Serpentine grasslands in the HCP study area are potential habitat for this
species.
Model Results
According to the model, 129 acres of fragrant fritillary primary habitat (less than
1% of the study area) and 112 acres of secondary habitat (less than 1% of the
study area) are found in the study area (Figure 2). All of the modeled habitat
occurs within SFPUC lands. Three of the four primary habitat areas are located
adjacent to or just north of Calaveras Reservoir. The fourth area occurs on a
hillslope drainage north of Upper Alameda Creek. Secondary habitat also occurs
on hillslope drainages north of Upper Alameda Creek.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
3
HCP Study Area
Species Range
0
100
MILES
FIGURE 1
Fragrant fritillary (Fritillaria liliacea)
Distribution
Source: CNDDB 2003
Figure 2 Habitat Distribution Model for Fragrant Fritillary (Fritillaria liliacea)
Legend
Ni
le
R
oa
d
Sunol
th
ill
R
ou
te
84
o
s R
ecito
V all
ad
/ R
Primary Habitat
Vallecito'
sC
A la
m
ree
ke
La
s
Canyon
Fo o
d
ro
80
I-6
e la L ag una
yo d
Ar
k
ed
e ek
De
l
n A
Re
Cr
ee
ni
o
Sa n
to
An
W
k
ill
ia
m
s
G
Stream
u
lc
Primary Road
Reservoir
Secondary Road
Study Area
h
La
st
Co
County Line
p
k
o
ee
rs
Cr
e
n
Cr e e k
p
dia
In
ad
s
SFPUC Ownership
k
Ro
yne
Ha
h
Gulc
lch
re e
id a n
aC
Sher
A
We
Fremont
Va
lle
o
I
Sa
ni
d
s Roa
alavera
C
y
lle
Va
nol
80
-6
ir
vo
n to
Su
se
r
a
Cr
Seconary Habitat
n
R
id
g
e
L
de
ey
n
ee
Cr
A lame
d a Cr
ee
k
Oa
la
Ca
0
I - 68
We
lle r
0
I-88
ve
Re
Roa d
Ri
se
rvo
e
0
Santa Clara Co.
ir
o
rt
Ho
ve
o
roy
Ar
P
y
h R
d
oa
Ma r s
Alameda Co.
dg
0.5
1
1:100,000
ras R oa d
r
F elte
k
ra s
Cal a ve
Milpitas
d
Ro a
©
k
nd
o
R
id
g
Calav
e
er
as
e
Cre
k
Mt.
Day
2
Miles
PLANTS
Most Beautiful Jewelflower (Streptanthus albidus ssp. peramoenus)
Most Beautiful Jewel-flower
(Streptanthus albidus ssp. peramoenus)
Status
Federal:
None
State:
None
California Native
Plant Society:
List 1B.2
Range
Most beautiful jewelflower (Streptanthus albidus ssp. peramoenus) is endemic to
the northern South Coast Ranges of Contra Costa, Alameda, and Santa Clara
Counties (California Native Plant Society 2008; California Natural Diversity
Database 2008). Recent genetic studies suggest that the range for most beautiful
jewelflower has not been resolved fully. Dark-flowered populations from near
Sunol, Mount Hamilton, and Henry Coe State Park, currently placed in
Streptanthus glandulosus (which has red-purple flowers), appear to be more
closely related to Streptanthus albidus subsp. peramoenus, which has lilaccolored flowers (Mayer et al. 1994; Mayer and Soltis 1999). The California
Natural Diversity Database (CNDDB) (2008) includes the dark-flowered
populations from near Sunol within its records for Streptanthus albidus subsp.
peramoenus. The range map for most beautiful jewelflower (Figure 1)
accommodates this expanded concept of the species and includes the darkflowered populations from Mount Hamilton, Henry Coe State Park, and
elsewhere.
The results of genetic studies suggest that flower color may not be a reliable
character for distinguishing between jewelflower species in the East Bay Area.
On the other hand, flower color has often been used to differentiate jewelflower
taxa (Kruckeberg 1958; Kruckeberg et al. 1982; Dolan and LaPre 1989). E. L.
Greene (1891) believed that the Mount Hamilton occurrences were sufficiently
distinct to warrant naming as Streptanthus mildredae, and it may be that these
dark-flowered populations should be recognized as a subspecies of Streptanthus
albidus.
Jewelflower populations in southern Monterey County and San Luis Obispo
County have also been treated as most beautiful jewelflower (California Natural
Diversity Database 2008), but the taxonomic position of these populations has
not yet been resolved (Mayer et al. 1994; California Native Plant Society 2008).
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
1
PLANTS
Most Beautiful Jewelflower (Streptanthus albidus ssp. peramoenus)
Occurrences within the HCP Study Area
The CNDDB (2008) contains two records of most beautiful jewelflower in the
HCP study area, one along Alameda Creek near its confluence with Calaveras
Creek, and one along Leyden Creek near its confluence with Alameda Creek.
The CNDDB records two other occurrences in Sunol Regional Wilderness
adjacent to the HCP study area. During surveys in May 2003, Jones & Stokes
botanists located the Leyden Creek occurrence and five additional occurrences of
most beautiful jewelflower in the HCP study area. Three of the new occurrences
are on the south-facing slopes north of Alameda Creek and represent additional
stands of the population that includes the two occurrences in Sunol Regional
Wilderness. One new occurrence was found in serpentine grasslands on the east
side of Calaveras Reservoir, about 0.5 mile south of the dam. Another new
occurrence was located in Arroyo Hondo, about 3.25 miles southeast of the dam.
The occurrence along Alameda Creek near its confluence with Calaveras Creek
could not be found; therefore, the exact location of this occurrence was not
determined.
Biology
Physical Description
Most beautiful jewelflower is an annual herb in the mustard family
(Brassicaceae). The plants are 60 to 100 centimeters tall and have bluish-green
foliage that is nearly hairless (Kruckeberg 1958; Buck et al. 1993). The blooming
period is between April and July (California Native Plant Society 2008). Flower
color is typically rose-lavender, although flower color varies among populations.
The populations in the study area are atypical, having dark purple petals more
typical of bristly jewelflower (Streptanthus glandulosus) or Tiburon jewelflower
(Streptanthus niger).
Habitat
Most beautiful jewelflower is almost entirely restricted to serpentinite outcrops or
soils derived from serpentinite. Serpentine soils are deficient in calcium, but
serpentine-endemic jewelflower populations are capable of growing under low
levels of calcium (Kruckeberg 1954). Most beautiful jewelflower is generally
found in grasslands dominated by native perennial grasses or in open grasslands
dominated by nonnative annual grasslands with relatively low cover of nonnative
grasses. It is also found on rock outcrops or grassy openings in serpentine
chaparral or where serpentine grassland or chaparral habitats transition to oak
woodland.
At least one population of the dark-flowered form of most beautiful jewelflower
occurs on non-serpentine habitat at Henry Coe State Park (Mayer et al. 1994). In
the HCP study area, the population found in Arroyo Hondo occurs in nonserpentine habitat, where it occurs on rock outcrops in coastal sage scrub
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
2
PLANTS
Most Beautiful Jewelflower (Streptanthus albidus ssp. peramoenus)
dominated by California sagebrush (Artemisia californica), bush monkeyflower
(Mimulus aurantiacus), and golden-yarrow (Eriophyllum confertiflorum). Bristly
jewelflower (Streptanthus glandulosus), to which most beautiful jewelflower is
closely related, also has serpentine-tolerant and serpentine-intolerant populations
(Kruckeberg 1951). Table 1 shows other species associated with most beautiful
jewelflower.
Table 1. Other Species Associated with Most Beautiful Jewelflower
Taxonomic name
Common Name
Nassella pulchra
Purple needlegrass
Dudleya setchellii
Santa Clara Valley dudleya
Plantago erecta
California plantain
Eschscholzia californica
California poppy
Cryptantha flaccida
Weak-stemmed cryptantha
Gilia tricolor
Bird’s-eye gilia
Eriogonum species
Wild buckwheat
Salvia columbariae
Chia
Clarkia species
Clarkia
Most beautiful jewelflower appears to be insect pollinated. Kruckeberg (1957)
reported that members of the Streptanthus glandulosus complex, including most
beautiful jewelflower, were incapable of self-pollination, and he had observed
bees, butterflies, and beetles visiting the flowers. Bees have been observed to the
primary floral visitors in other outcrossing Streptanthus species (Dieringer 1991;
Preston 1994), although flies and butterflies also visit Streptanthus flowers
(Moldenke 1976). Streptanthus flowers appear to be self-fertile, but a
combination of spatial and temporal separation of the stamens and receptive
stigmas presents self-pollination (Preston 1991).
No information on herbivory of most beautiful jewelflower was available;
however, other jewelflower species are eaten by herbivorous insects. The larvae
of pierid butterflies commonly eat jewelflower leaves, flowers, and developing
fruit (Shapiro 1981a, 1981b, 1984, Karban and Courtney 1987). The flowers are
also eaten by sap beetles and flea beetles (Shapiro 1981a; Karban and Courtney
1987; Preston 1991). Some species of serpentine-endemic jewelflowers appear to
have “egg-mimics” on the leaves, which inhibit some pierid species from laying
eggs there (Shapiro 1981a).
Population Trend
Global:
Unknown
State:
Unknown
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
3
PLANTS
Most Beautiful Jewelflower (Streptanthus albidus ssp. peramoenus)
Within HCP Unknown
Study Area:
Threats
Potential threats to most beautiful jewelflower include cattle grazing, competition
from invasive exotic species, and habitat loss from residential development and
road construction (California Natural Diversity Database 2008).
Indirect impacts on most-beautiful jewelflower from Plan implementation could
include increased dust, livestock and human disturbance, spread of nonnative
invasive species, change in fire regime, and changes to surface hydrology.
Overall, however, implementation of the HCP is expected to have a net benefit
on the most-beautiful jewelflower because of the improved habitat and
population management.
Data Characterization
The location database for most beautiful jewelflower includes 80 data records
from 1938 to 2006 (California Natural Diversity Database 2008). Forty-one
occurrences were documented in the previous 10 years. All occurrences are
believed to be extant. Many are of high precision and may be accurately located,
including those within the HCP study area. Three other occurrences are known
that are not recorded in the CNDDB: two populations of the dark-flowered form
that occur on Mount Hamilton and at Henry Coe State Park (Mayer et al. 1994)
and a third population of the dark-flowered form that occurs in Del Puerto
Canyon, in western Stanislaus County (Preston personal observation). Other
collections of Streptanthus glandulosus from the Mount Hamilton Range
(CalFlora 2008) may also represent the dark-flowered form of most beautiful
jewelflower.
Very little specific information is available for most beautiful jewelflower,
although much general information is available for other jewelflower species in
the scientific literature. The main sources of general information on most
beautiful jewelflower are The Jepson Manual (Hickman 1993) and the California
Native Plant Society (2008). Specific information on the systematics of most
beautiful jewelflower is found in Mayer et al. (1994) and in Mayer and Soltis
(1999). Specific observations on habitat and plant associates, threats, and other
factors are provided in the CNDDB (2008).
Model Description
Model Assumptions
1. Primary habitat: Serpentine grassland and serpentine foothill pine-chaparral
woodland below 2,000 feet.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
4
PLANTS
Most Beautiful Jewelflower (Streptanthus albidus ssp. peramoenus)
2. Secondary habitat: Serpentine grassland above 2,000 feet and Diablan sage
scrub below 3,600 feet.
Model Rationale
Most-beautiful jewelflower is almost entirely restricted to serpentinite outcrops
or soils derived from serpentinite. Most-beautiful jewelflower is generally found
in grasslands dominated by native perennial grasses or in open annual grasslands
with relatively low cover of non-native grasses (California Natural Diversity
Database 2008). It most often occurs at elevations below 2,000 feet (California
Natural Diversity Database 2008), but it has been collected from locations as
high as 3,640 feet. It is also found on rock outcrops or grassy openings in
serpentine chaparral or where serpentine grassland or chaparral habitats transition
to oak woodland. At least one population occurs in non-serpentine habitat in
coastal sage scrub.
Model Results
According to the model, 285 acres of modeled primary habitat and 1,721 acres of
secondary habitat are found in the study area (Figure 2). All primary and
secondary habitat is found within SFPUC lands. The primary habitat is located
near the headwaters of a drainage on the hillslopes just north of Upper Alameda
Creek. Secondary habitat occurs adjacent to the primary habitat, as well as in the
serpentine grassland adjacent to and east of the Calaveras Reservoir, and west of
the confluence of Calaveras and Alameda Creeks, extending north of Leyden
Creek’s confluence with Alameda Creek. Most of the secondary habitat occurs in
three general areas of Diablan sage scrub. One of these areas is north of Arroyo
Hondo. One area consists of small patches west of Alameda Creek, downstream
of the confluence with Calaveras Creek. The third and largest area is found along
San Antonio, La Costa, and Indian Creeks. Four of the five occurrences found
during the 2003 survey are located in areas predicted to be secondary habitat. The
other occurrence is just outside the study area, where we did not apply the model.
One of the two occurrences recorded in the CNDDB is found outside of modeled
habitat. This occurrence is located just south of the confluence of Calaveras and
Alameda Creeks. Jones and Stokes botanists were not able to relocate it during
the 2003 survey. This occurrence of most-beautiful jewelflower outside of
modeled habitat underscores the limitations of the model. Available data does not
indicate that the grasslands at the confluence of Alameda and Calaveras Creeks
are on serpentine soils. Available serpentine soils data are at too coarse a scale to
accurately model all habitat, but the model does capture almost all of the known
occurrences of most-beautiful jewelflower in the study area.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
5
HCP Study Area
Species Range
0
100
MILES
FIGURE 1
Most-beautiful jewel flower (Streptanthus albidus ssp. peramoenus)
Distribution
Source: CNDDB 2003
Figure 2 Habitat Distribution Model for Most-beautiful Jewelflower (Streptanthus albidus ssp. peramoenus)
Legend
Ni
le
R
oa
d
Sunol
th
R
ill
ou
te
84
o
s R
ecito
V all
Vallecito'
sC
A la
m
ree
ad
Primary Habitat
/ R
Seconary Habitat
ke
La
s
Canyon
Fo o
d
ro
80
I-6
e la L ag una
yo d
Ar
k
Known Occurrence
ed
e ek
n A
Re
Cr
ee
ni
o
Sa n
to
An
W
k
ill
ia
m
s
G
Stream
u
lc
Primary Road
Reservoir
Secondary Road
Study Area
h
La
st
Co
County Line
p
k
o
ee
rs
Cr
e
n
Cr e e k
p
dia
In
ad
s
SFPUC Ownership
k
Ro
yne
Ha
h
Gulc
lch
re e
id a n
aC
Sher
A
We
Fremont
Va
lle
o
I
Sa
De
l
ni
d
s Roa
alavera
C
y
lle
Va
nol
80
-6
ir
vo
n to
Su
se
r
a
Cr
n
R
id
g
e
L
de
ey
n
ee
Cr
A lame
d a Cr
ee
k
Oa
la
Ca
0
I - 68
We
lle r
0
I-88
ve
Re
Roa d
Ri
se
rvo
e
0
Santa Clara Co.
ir
o
rt
Ho
ve
o
roy
Ar
P
y
h R
d
oa
Ma r s
Alameda Co.
dg
0.5
1
1:100,227
ras R oa d
r
F elte
k
ra s
Cal a ve
Milpitas
d
Ro a
©
k
nd
o
R
id
g
Calav
e
er
as
e
Cre
k
Mt.
Day
2
Miles
REPTILES
Alameda Whipsnake (Masticophis lateralis euryxanthus)
Alameda Whipsnake
(Masticophis lateralis euryxanthus)
Status
State:
Threatened
Federal:
Threatened
Critical Habitat:
Final designation issued in October 2006
(71:190 FR 58175).
Range
The Alameda whipsnake (Masticophis lateralis euryxanthus) is a subspecies of
the California whipsnake (Masticophis lateralis). The North American
distribution for the California whipsnake includes northern California west of the
Sierran Crest and desert to central Baja California (Figure 1). This species is
absent from the floor of the Central Valley, and its California distribution
parallels that of chaparral habitat (Stebbins 2003).
Historically, the Alameda whipsnake occupied suitable habitat in Alameda,
Contra Costa, and possibly western San Joaquin and northern Santa Clara
Counties (U.S. Fish and Wildlife Service 2002). The current distribution of the
Alameda whipsnake has been described as five populations within a fragmented
regional metapopulation in Alameda and Contra Costa Counties: Tilden-Briones,
Oakland–Las Trampas, Hayward–Pleasanton Ridge, Mount Diablo–Black Hills,
and Sunol–Cedar Mountain (U.S. Fish and Wildlife Service 2002). The HCP
study area lies within the last listed recovery unit and the connecter unit between
the Hayward-Pleasanton Ridge and Sunol—Cedar Mountain Unit.
The Sunol-Cedar Mountain has been previously thought to be the southern
portion of the range of the Alameda Whipsnake and an area of intergradation
between the Alameda Whipsnake and the chaparral whipsnake (Masticophis
lateralis lateralis ) (Riemer 1954; Jennings 1983). A draft report providing a
preliminary analysis of the genetics of the California whipsnake now indicates
that the California whipsnake can be divided into 4 genetic groups called clades
(not necessarily subspecies) (Mustin pers. comm.) 1. The genetic analysis
indicates the clade of M. lateralis that occurs in Alameda and Contra Costa
Counties also occurs in Santa Clara County and as far south as San Benito and
Monterey Counties, with the southern boundary coinciding with an area that was
formerly inundated by the San Joaquin Embayment.
1
Letter from Cori Mustin, U.S. Fish and Wildlife Service, October 10, 2010.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
1
REPTILES
Alameda Whipsnake (Masticophis lateralis euryxanthus)
Occurrences within the HCP Study Area
Surveys for Alameda whipsnake have not been conducted in the San Francisco
Public Utilities Commission (SFPUC) HCP study area. There is one California
Natural Diversity Database (CNDDB) occurrence in the HCP study area, located
in the Sunol Wilderness near the confluence of Alameda Creek and Calaveras
Creek (California Natural Diversity Database 2008). Additionally, sightings have
been recorded within the Alameda watershed (San Antonio Reservoir) from as
early as the 1970s. Many of these sightings were recorded as Alameda
whipsnake, intergrades, or unknown (California Natural Diversity Database
2008), but would be considered part of the clade that includes M. lateralis
euryxanthus under the previously cited recent genetic analysis. A population of
Alameda whipsnake is also believed to exist in Sunol Regional Park (U.S. Fish
and Wildlife Service 2002).
The HCP study area lies completely within Sunol–Cedar Mountain Recovery
Unit 5, as described by the USFWS (2002). The SFPUC HCP study area makes
up 23% of Unit 5. A potential movement corridor between Sunol–Cedar
Mountain population and the Hayward–Pleasanton Ridge population occurs
within the Alameda watershed, at Alameda Creek. Movement corridors are
critical to the recovery of this species because they allow for gene flow between
populations.
USFWS designated critical habitat for Alameda whipsnake in March 2000
(65 FR 12155). The critical habitat designation was challenged in court and
withdrawn as a result of a court order in May 2003. A new draft rule of critical
habitat was published in October 2005 (70 FR 60607) and reopened for comment
on May 4, 2006 (71 FR 26311). This critical habitat designation was finalized on
October 2, 2006 (71 FR 58175). Critical Habitat Unit 5B falls partially within the
HCP study area. This unit comprises 18,214 acres in Alameda and Santa Clara
counties, eastward from just north of Calaveras Reservoir, including Wauhab
Ridge and Oak Ridge, of which 7,904 acres falls within the study area. Alameda
Creek is located at the west margin of the unit. As a result of recent genetic
studies that were previously cited, there may be changes in areas designated as
critical habitat.
Biology
Habitat
The Alameda whipsnake occurs primarily in coastal scrub and chaparral
communities, but also forages in a variety of other communities in the inner
Coast Range, including grasslands and open woodlands (Swaim 1994). Rock
outcrops with deep crevices or an abundance of rodent burrows are important
habitat components for overnight dens, refuges from predators and excessive
heat, and foraging (Swaim 1994). According to USFWS (2006), suitable habitat
for this species includes communities that support mixed chaparral, coastal scrub,
and annual grassland and oak woodlands adjacent to scrub habitats. Grassland
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
2
REPTILES
Alameda Whipsnake (Masticophis lateralis euryxanthus)
areas linked to scrub by rock outcrops or river corridors are also considered
primary constituent elements (U.S. Fish and Wildlife Service 2006).
The Alameda whipsnake is most abundant in open (and partially open), lowgrowing shrub communities. This habitat provides cover for snakes during
dispersal, shelter from predators, and a variety of microhabitats where
whipsnakes can move to regulate their body temperature (Swaim 1994).
Whipsnakes exhibit a high degree of stability and a high mean activity in body
temperature (33.4 degrees centigrade). Their habitat must consist of a mix of
sunny and shady sites to provide a range of temperatures for their activities
(Swaim 1994; U.S. Fish and Wildlife Service 2006). A sparse shrub canopy is
ideal because it provides a visual barrier to potential avian predators (Swaim
1994).
Other important habitat features include small mammal burrows, rock outcrops,
talus, and other forms of shelter that provide snakes with alternative habitats for
temperature regulation, protection from predators, sites for egg-laying, and
winter hibernaculum (winter residence where the snakes hibernate). Alameda
whipsnakes spend November through March in a winter hibernaculum (U.S. Fish
and Wildlife Service 2006).
Home-range size for male snakes in Alameda and Contra Costa counties (Tilden
Park and Moller Ranch) varies in size from 1.9 to 8.7 hectares (ha) (mean =
5.5 ha). Home-range size for female snakes was 3.9 and 2.9 hectares (Swaim
1994). When movements of individual snakes (two males and one female) were
monitored in these areas, results indicated that most of the home range was not
used. Both male and female snakes repeatedly returned to core retreat areas
within their home range after intervals of nonuse. These snakes did exhibit
overlap in use of these relatively large home ranges (Swaim 1994).
Breeding Habitat Requirements
Mating occurs from late March through mid-June (U.S. Fish and Wildlife Service
2006). Whipsnakes lay a clutch of six to 11 eggs (Stebbins 2003), probably in
loose soil or under logs or rocks (Zeiner et al. 1988). According to Swaim
(1994), female Alameda whipsnakes will use grassland habitat for egg laying.
Little else is known about habitat requirements for breeding and egg laying
(Zeiner et al. 1988). Swaim (1994) documented that courtship and mating occur
near the female’s hibernaculum. During the breeding season, male snakes exhibit
more movement throughout their home range, while female snakes remain
sedentary from March until egg laying (Swaim 1994).
Foraging Requirements
In general, whipsnakes prey on a variety of vertebrate species, including frogs,
lizards, nestling birds, and rodents (Zeiner et al. 1988). Studies indicate that
lizards are an important prey item. Occupied areas usually support a prey base of
at least two lizard species, especially the western fence lizard (Sceloporus
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
3
REPTILES
Alameda Whipsnake (Masticophis lateralis euryxanthus)
occidentalis) (Stebbins 2003), and whipsnake populations thrive when lizards are
abundant (McGinnis 1992 in U.S. Fish and Wildlife Service 2002).
Rock outcrops are particularly important foraging habitat for the Alameda
whipsnake because they support many of the species’ prey (U.S. Fish and
Wildlife Service 2006). Additionally, the Alameda whipsnake has been observed
foraging in grassland habitats adjacent to native Diablan sage scrub habitats
(Swaim 1994).
Demography
There have been no studies of the demography or longevity of Alameda
whipsnakes. Captive individuals have lived up to ten years. (U.S. Fish and
Wildlife Service 2002.)
Dispersal
The Alameda whipsnake is nonmigratory. There is little information on patterns
of dispersal in this species. There is evidence of site fidelity in this species, at
least for many adults. Swaim (1994) observed evidence of individual snakes
using the same home range in successive years. More recent trapping surveys
(2000–2003) have shown multiple Alameda whipsnake using the same general
area for three successive years (Swaim pers. comm.).
Behavior
The Alameda whipsnake is a fast-moving, diurnal predator that forages actively
on the surface (Zeiner et al. 1988). Alameda whipsnakes have two seasonal peaks
in activity, one during the spring mating season and the other during late summer
and early fall. During the first peak in activity, males will move throughout their
home range, while females remain close to their hibernaculum. Male movement
appears to be associated with foraging and searching for mates. Females exhibit a
peak in activity only for a few days during the spring when they move to an area
outside their normal range, presumably to find egg-laying sites (Swaim 1994).
After reproductive activities are completed, male and female movements resume
similar patterns. In late-June and July, both males and females exhibit decreased
activity levels, though evidently this species does not estivate during the summer
months (Swaim 1994). The second peak in seasonal activity occurs in late
summer and fall. During this time, Swaim (1994) recorded activity in both
hatchling and adult snakes, possibly in response to an increase in the availability
of prey (hatchling lizards).
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
4
REPTILES
Alameda Whipsnake (Masticophis lateralis euryxanthus)
Ecological Relationships
Diurnal predators, especially raptors, prey on adult Alameda whipsnakes, and
nocturnal mammals likely prey on their eggs (Zeiner et al. 1988). Basking in
open terrain may expose snakes to predators such as red-tailed hawks (Fitch 1949
in Swaim 1994).
Data Characterization
The USFWS published a draft recovery plan for the Alameda whipsnake in
November 2002. According to this plan, recovery of Alameda whipsnake
populations will require a combination of long-term research/management and
immediate management actions. The USFWS lists the Sunol–Cedar Mountain
population of the Alameda whipsnake as having a high potential for recovery—
with active management, habitat restoration and mitigation for incompatible land
uses (U.S. Fish and Wildlife Service 2002). Incompatible land uses include fire
suppression, off-road vehicle use, grazing practices, unauthorized collecting, and
mining.
Additionally, the USFWS designated critical habitat for this species in
October 2006 (71 FR 58175).
Population Trend
Global:
Declining
State:
Declining
Within HCP Unknown
Study Area:
Threats
Throughout western Contra Costa and Alameda Counties, Alameda whipsnake
populations have declined from loss of habitat resulting from urban expansion
(U.S. Fish and Wildlife Service 2006). Urban development, particularly road and
highway construction, has also fragmented Alameda whipsnake populations and
made them more vulnerable to extinction (U.S. Fish and Wildlife Service 1997).
Development adjacent to whipsnake habitat increases the likelihood of predation
from feral cats and injury or death from public recreational use (U.S. Fish and
Wildlife Service 1997).
Within the southeast portion of their range, Alameda whipsnake populations are
threatened by fire suppression (increasing the potential for catastrophic
wildfires), gravel mining, grazing practices, off-road vehicle use, and
unauthorized collection. Additionally, the Alameda watershed contains barriers
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
5
REPTILES
Alameda Whipsnake (Masticophis lateralis euryxanthus)
to whipsnake movement. Existing barriers include a high concrete barrier south
of Niles Canyon Road and north of Alameda Creek, railroad tracks, and heavy
traffic on Niles Canyon Road. All three physical barriers potentially present
threats to the survival of this species.
The USFWS identified catastrophic wildfire as a threat to the Sunol–Cedar
Mountain population (U.S. Fish and Wildlife Service 2002). Fire suppression
alters suitable Alameda whipsnake habitat in two important ways. First, it
increases the chances of large catastrophic fires occurring in areas where
vegetation has become overgrown. A buildup of flammable fuel loads in
Alameda whipsnake habitat can lead to high-intensity fire events that may be
detrimental to this species. Second, fire suppression leads to a closed scrub
canopy that generally tends to reduce the diversity of microhabitats that
whipsnakes require (Swaim 1994). However, more recent studies have shown
that whipsnakes can occur in high numbers in certain communities (e.g. chamise
chaparral) that are fairly closed-canopy and have not burned for decades.
Unauthorized collection of specimens may be more of a threat in the HCP study
area because of the abundance of native reptiles and remote roads, both of which
attract enthusiasts and collectors (U.S. Fish and Wildlife Service 2002).
O&M activities such as road use, road construction, fence installation and repair,
vegetation management around roads, and recreation on SFPUC lands may
impact whipsnakes in the Alameda Creek Watershed. Road construction would
permanently remove habitat. Temporary impacts from vegetation management
and recreational use could include temporary cutback of vegetation along roads
and presence of human activity, including vehicle traffic along maintenance
roads. Traffic could cause direct mortality.
Indirect impacts on Alameda whipsnake snake include disturbance from
increased traffic and human disturbance, as well as potential changes in fire
regime. Changes in fire regime result in changes in scrub and chaparral
vegetation. Reduction in fire intervals may reduce or eliminate the amount of this
type of vegetative cover; increases in fire intervals results in a dense growth that
reduces sun exposure necessary for this snake, and may allow the addition of
trees that can transform the habitat into woodland unsuitable for this species.
The newly constructed roads and bridges have the potential to attract snakes to
the heat stored in the road, which could increase mortality and predation from
natural predators or from vehicle use.
Modeled Species Distribution in HCP Study Area
Methods Unique to this Species
The Alameda whipsnake model was developed using two stages. The first stage
of analysis involved identifying core habitat using the Jones & Stokes land cover
map. At this level of analysis, all Diablan sage scrub habitat and willow
forest/scrub located on the land cover map (i.e., patches greater than the
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
6
REPTILES
Alameda Whipsnake (Masticophis lateralis euryxanthus)
minimum mapping unit of 1 acre) were delineated as core habitat for this species.
The second stage of analysis was conducted by Swaim Biological Consulting and
focused on identifying other types of core habitat for this species. Unlike the first
stage of analysis that relied solely on the land cover map, Swaim biologists used
2002 aerial photographs of the study area to identify patches of core whipsnake
habitat that were not directly linked to a specific mapped landcover type.
Examples of core whipsnake habitat that were identified during this finer level of
analysis included patches of Diablan sage scrub less than 1 acre in size as well as
other scrub or brush patches of various sizes that could provide suitable core
habitat. Thus, suitable core habitat was defined broadly to include patches of
vegetation dominated by either Diablan sage scrub, California sagebrush
(Artemisia californica), mule fat (Baccharis salicifolia), lupine (Lupinus sp.),
willows (Salix sp.), or vegetation that structurally appeared like a shrub
community. Ground truthing was not conducted during this analysis.
Analysis of aerial photographs and the land cover map allowed Swaim biologists
to conclude that most of the non-core habitat within the study area could be used
as movement habitat for this species (Swaim pers. comm.). Whipsnakes will use
grasslands, woodlands, riparian zones and the fringes of developed or disturbed
land cover types to move from one core area to another. Because of the
abundance of potential movement habitat for this species within the study area,
movement habitat was not modeled for this species. The most likely movement
corridors are creeks and drainages with or without riparian vegetation and rocky
areas. Although the model does not describe general movement habitat, it does
identify three specific movement corridors that allow movement in areas
otherwise restricted by development.
Model Description
Model Assumptions
1. Core Habitat: Core habitat for Alameda whipsnake is defined as home range
areas in which individuals usually find shelter, breed, hibernate, and spend
the majority of their time foraging. All Diablan sage scrub and willow
riparian woodland/scrub within the study area was considered core habitat
for Alameda whipsnake. All areas mapped by Swaim Biological Consulting
as isolated patches of scrub of any type were also considered suitable core
habitat. In addition, a perimeter zone of all adjacent grassland, oak savannah
and oak woodland within 500 feet of the suitable scrub areas, regardless of
the size of the scrub patch, was also considered core habitat for this species.
2. Movement Habitat. A majority of the Alameda watershed is potential
movement habitat for the Alameda whipsnake; however, there are three areas
within the HCP study area where movement habitat may be critical to the
species. These include Alameda Creek, Vallecitos Creek and isolated
grassland areas along Calaveras Road. At Alameda and Vallecitos Creeks the
entire riparian corridor, including creek beds and adjacent vegetation, are
considered important movement habitat for the Alameda whipsnake.
Alameda creek where it crosses under I-680 may be the only remaining
viable movement route between the subpopulation of whipsnakes on either
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
7
REPTILES
Alameda Whipsnake (Masticophis lateralis euryxanthus)
side of I-680 (the Sunol-Cedar Mountain subpopulation and the Hayward
Pleasanton Ridge subpopulation). Vallecitos Creek links Pleasanton Ridge
and San Antonio Reservoir. The grassland areas adjacent to Calaveras Road
connect important core habitat areas on either side of Calaveras Road.
Model Results
Figure 2 shows the modeled suitable core habitat for the Alameda whipsnake
within the HCP study area. Core habitat covers approximately 16,719 acres.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
8
HCP Study Area
Breeding Range
0
100
MILES
FIGURE 1
Alameda Whipsnake (Masticophis lateralis euryxanthus)
Distribution
Source: USFWS 2002
Figure 2 Habitat Distribution Model for Alameda Whipsnake (Masticophis lateralis euryxanthus)
Legend
R
ll
te
ou
1
Vallecito'
sC
m
#
Al a
ed
Core Habitat
k
a
Cr
ree
/ R
er
C
W
ill
ia
m
Known Occurrence
s
Stream
G
u
lc
Reservoir
Secondary Road
Study Area
h
Primary Road
e
rs
k
ee
#
Cre e k
p
Cr
lc h
n
We
p
SFPUC Ownership
dia
In
A
ad
s
ne
Hay h
Gulc
County Line
k
ee
Cr
Ro
Fremont
re
ek
a
os t
id a n
#
ni
o
#
nt o
Va
l le
C
La
She r
3
n A
o
ni
A
Sa n
Road
veras
I
Sa
Approximate movement cooridor areas
where movement is constrained by
development or other areas
1 - Vallecitos Creek
2 - Alameda Creek
3 - Calaveras Road
De
l
nt o
Cala
y
lle
Va
nol
-
0
68
ir
vo
Re
s
Su
#
eek
2
#
Fo o
Sunol
d
thi
#
Ni
les
oa
ad
ke
La
R
Ro
os
ecit
Va ll
#
Canyon
84
a
de la L a gun
d
o
roy
80
I-6
Ar
on
R
id
g
e
L
de
ey
n
ee
Cr
k
A lame
d a Cr
ee
k
Ca
ve
la
0
I - 68
We
lle r
0
I-88
Re
R oa d
se
rvo
dg
Alameda Co.
e
Santa Clara Co.
o
o
rt
h R
Mars
Ho
ve
roy
Ar
P
y
d
oa
r
Felte
Ri
ir
as R oa d
Milpitas
d
Ro a
k
ra s
r
Ca la ve
nd
o
R
id
g
Calav
as
e
er
©
ek
C re
5/5/08
H:\gis\projects\sfpuc\sfp01.02\arcmap\whipsnake_modified_NJ_no_sec_hab.mxd
04.15.04
Oa
Mt.
Day
1
0
1
Miles
REPTILES
Western Pond Turtle (Actinemys marmorata)
Western Pond Turtle (Actinemys marmorata)
Status
State:
Species of Special Concern
Federal:
None
Critical Habitat:
N/A
Range
Western pond turtle is the only species in its genus that occurs in the western
United States. Western pond turtle’s northern distribution includes Puget Sound
in Washington south through the Oregon River drainage in central California,
generally west of the Cascade-Sierra crest to the American River. Today, western
pond turtle occurs in 90% of its historic range in the Central Valley and west of
the Sierra Nevada—but in greatly reduced numbers (Jennings and Hayes 1994)
(Figure 1).
Occurrences within the HCP Study Area
Extant populations of the western pond turtle are known to occur within the HCP
Study Area. During a pond survey conducted by Jones & Stokes (now ICF
International) and San Francisco Public Utilities Commission (SFPUC) in
September 2003 biologists observed western pond turtles in ponds M4, M9, M33,
and J24. In addition, this species is known to breed in the Calaveras Reservoir,
and has been observed in three ponds east of Calaveras Reservoir and on a single
pond southeast of San Antonio Reservoir (Tim Koopman pers. comm.).
According to the California Natural Diversity Database (CNDDB) there are five
documented observations of western pond turtle within the HCP study area
(California Natural Diversity Database 2010).
Biology
Habitat
Western pond turtles occur in a variety of aquatic habitats from sea level to
elevations of 1,980 meters (6,500 feet). They are found in rivers, streams, lakes,
ponds, wetlands, reservoirs, and brackish estuarine waters. (Holland 1994;
Jennings and Hayes 1994.) Western pond turtles use aquatic habitats primarily
for foraging, thermoregulation, and avoidance of predators. They prefer aquatic
habitats with large areas for cover (logs, algae, vegetation) and basking sites
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
1
REPTILES
Western Pond Turtle (Actinemys marmorata)
(boulders or other substrates) and have been observed to avoid areas of open
water lacking these habitat features (Holland 1994). The turtles use basking sites
for thermoregulation. Western pond turtles can be found in waters with
temperatures as low as 1ºC (34ºF) or as high as 39–40ºC (102–104ºF) (Jennings
and Hayes 1994).
Western pond turtles overwinter in both aquatic and terrestrial habitats. Aquatic
refugia consist of rocks, logs, mud, submerged vegetation, and undercut areas
along banks. Terrestrial overwintering habitat consists of burrows in leaf litter or
soil (Davis 1998). The presence of a duff layer seems to be a general
characteristic of overwintering habitat. Upland nesting sites must be dry and
often have a high clay or silt fraction. Gravid females leave drying creeks in June
to oviposit in sunny upland habitats, including grazed pastures. Nesting has been
reported to occur up to 402 meters (1,391 feet) from water (Jennings and Hayes
1994), but is usually closer, averaging 28 meters (92 feet) from aquatic habitat
(Rathbun et al. 2002).
Foraging Requirements
Western pond turtles are omnivorous feeders, opportunistic predators, and
occasional scavengers (Holland 1985a, 1985b; Bury 1986). The majority of their
diet consists of crustaceans, midges, dragonflies, beetles, stoneflies, and
caddisflies, but pond turtles also feed on mammal, bird, reptile, amphibian, and
fish carrion. Western pond turtles will eat plant matter and have been observed
foraging on willow and alder catkins and on ditch grass flowers (Holland 1991b).
Plant foods may provide an important source of readily available nutrients for
adults and some proteins when animal food is unavailable. Adults, especially
females, consume a greater percentage of plant material than juveniles (Bury
1986).
Reproduction
Western pond turtles first breed at 10–14 years of age (U.S. Fish and Wildlife
Service 1999). Most females lay eggs in alternate years. Clutch size ranges from
one to 13 eggs, with larger females generally laying larger clutches (Holland
1985a, 1991a). Females move 12–402 meters (39–1,319 feet) into upland
habitats to nest from May through July. Sparsely vegetated, sunlit nesting sites
are preferred and they are known to be found in active pasture and agricultural
fields (Crump 2001). Incubation lasts 80–100 days, and the normal hatch success
is approximately 70%. Nest predation rates are high and complete failure of nests
is common. In southern California, juveniles emerge from the nest in early fall
(Holland 1994). Most hatchlings overwinter in the nest and move to water in
March and April, although some leave the nest in September (Holland 1985a,
1991a, 1991b).
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
2
REPTILES
Western Pond Turtle (Actinemys marmorata)
Demography
Survivorship in western pond turtles is apparently dependent on age and sex.
Hatchlings and first-year juveniles average only 8–12% survivorship; this rate
may not increase significantly until turtles are 4–5 years old (U.S. Fish and
Wildlife Service 1999). Once the turtles reach adult size, survivorship increases
dramatically, with an average adult turnover rate of only 3–5%. Adult males
generally have a higher probability of survivorship than adult females, with
skewed sex ratios reaching 4:1 (males to females). The apparent cause for this
difference is a higher mortality experienced by females from predation during
overland nesting attempts (Holland 1991a).
Behavior
Western pond turtles are not known to be territorial; aggressive encounters—
including gesturing and physical combat (Bury and Wolfheim 1973)—are
common, and may function to maintain spacing on basking sites and to settle
disputes over preferred spots. Competing individuals may push and ram each
other, threaten one another with open-mouthed gestures, and occasionally bite
one another.
Measured home ranges of western pond turtles average 1 hectare (2.5 acres) for
males, 0.3 hectare (0.7 acre) for females, and 0.4 hectare (1 acre) for juveniles
(Bury 1972a). Males generally move farther than females or juveniles (Bury
1972a), but there is little movement between drainages (Holland 1991b).
Western pond turtles commonly forage in late afternoon or early evening. They
also bask intermittently throughout the day to maintain a body temperature of
24–32°C (75–90°F). In general, these turtles typically become more active in
water that consistently reaches 15°C (60°F) (Jennings and Hayes 1994). They
avoid extreme heat by moving to cooler areas on the bottom of pools.
In some parts of their range, western pond turtles are seasonally active,
overwintering from October and November through March and April. However,
in the Central Valley and along the California coast, they may be active
throughout the year (Holland 1991a).
Ecological Relationships
Introduced species have altered the ecological conditions of many areas inhabited
by western pond turtles. Bullfrogs and warm water fish are significant predators
on hatchlings and small juvenile western pond turtles. Sunfish compete for
invertebrate prey. Carp can cause turbidity (Lampman 1946), which can
influence the densities of zooplankton important in the diet of hatchlings and
young turtles (Holland 1985b). Introduced turtles, such as sliders, snapping
turtles (Chelydra serpentina), and painted turtles may compete with pond turtles,
exposing them to diseases for which they have no resistance (Hayes et al. 1999).
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
3
REPTILES
Western Pond Turtle (Actinemys marmorata)
In California, Oregon, and Nevada, 17 species of exotic aquatic or semiaquatic
turtles have been found in pond turtle habitats (Holland and Bury 1998).
Population Trend
Global:
Declining [Bury 1986]
State:
Unknown
Within HCP Unknown
Study Area:
Threats
Numerous factors, including loss, degradation, and fragmentation of habitat;
disease; introduced predators and competitors; and other natural and
anthropogenic conditions present ongoing threats to western pond turtle
throughout 75–80% of its range. (U.S. Fish and Wildlife Service 1999; Holland
1991a.)
Recent studies describe populations that have adults but few juveniles, indicating
that little or no recruitment is taking place. Because pond turtles are long-lived,
nonreproducing populations may persist in isolated wetlands long after
recruitment of young has ceased (Holland 1991a; U.S. Fish and Wildlife Service
1999).
Specific threats to populations of this species in the Alameda watershed include
agricultural activities and livestock grazing. Western pond turtle nesting sites
could be affected during the incubation period by agricultural or livestock
grazing activities, leading to annual nesting failures (Jennings and Hayes 1994).
Cattle trample and eat aquatic vegetation that serves as habitat for hatchlings, and
they may crush pond turtle nests (Hayes et al. 1999). Furthermore, agricultural
diversions have resulted in the elimination of pond turtles from such streams as
well as isolation of turtle populations located in other portions of affected
drainages (Holland 1991a).
Direct impacts on western pond turtle from SFPUC activities would be primarily
from water filtration and transmission system operations and maintenance
(O&M) activities that would affect the hydrologic regime in streams below the
dams but could also include road construction, road use, fence construction
maintenance and repair, and vegetation management on and around roads. Dam
and water facility operation activities include controlled releases such as fishery
management releases. Direct impacts on western pond turtle aquatic foraging
habitat from scheduled releases for instream flows could occur due to reduced
flows during November through May, resulting in narrower stream widths
downstream of Calaveras and Turner Dams, which would reduce foraging and
breeding habitat in Calaveras, San Antonio, and Alameda Creeks.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
4
REPTILES
Western Pond Turtle (Actinemys marmorata)
Indirect effects on streams or ponds, including increased runoff and spread of
nonnative plants, can adversely affect turtles. Recreational activities could
increase human disturbance, collection, and new roads could cause increased
vehicle-related disturbance. Human disturbance may directly harm species
(through collection) or cause disruption of nesting or other essential life-history
behaviors.
Data Characterization
As mentioned above, there are five CNDDB occurrences for western pond turtle
within the HCP study area. All of these records date from 1993 or later. Three of
these occurrences are for turtles in stock ponds on private lands, East Bay
Regional Parks and Recreation District (EBRPD) lands, and San Francisco
International Airport (SFO) City/County lands. The two remaining occurrences
are for pond turtles within Alameda Creek on lands of unknown ownership
(California Natural Diversity Database 2010).
Currently, the sizes and densities of western pond turtle populations in California
are not well known. Information on dispersal, population structure, population
dynamics, and the nature and dynamics of environmental factors affecting
populations (including edge effects) is needed to effectively design and
implement conservation plans. In addition, the current genetic diversity of
existing populations should be investigated to determine metapopulation status,
gene flow between populations, and long-term population viability.
Modeled Species Distribution in HCP Study Area
Figure 2 shows habitat distribution model for the western pond turtle within the
46,700-acre study area.
Model Description
Model Assumptions
1. Perennial ponds and streams in all land cover types (including: valley
needlegrass grassland, non-native grassland, serpentine bunchgrass
grassland, Serpentine Foothill Pine-Chaparral Woodland, mixed evergreen
forest/oak woodland, valley oak woodland, blue oak woodland, oak savanna,
central coast live oak riparian forest, coast live oak riparian forest, sycamore
alluvial woodland, willow riparian forest/scrub, white alder riparian forest,
urban/developed, Diablan sage scrub, freshwater marsh, nursery, turf,
serpentine foothill pine, and cultivated agriculture land-cover types) were
considered aquatic (core) habitat for western pond turtles.
2. The shoreline of Calaveras Reservoir and San Antonio Reservoir provide
aquatic (core) habitat for this species (50-feet out from shoreline).
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
5
REPTILES
Western Pond Turtle (Actinemys marmorata)
3. All areas within a 100-foot radius of core aquatic habitat, excluding
freshwater marsh, nursery, turf, and serpentine foothill pine are considered
suitable (core) nesting habitat for western pond turtles.
4. All seasonal streams provide suitable movement habitat for western pond
turtles, and areas within 300-feet of seasonal streams and ponds provide
suitable overwintering habitat for this species, excluding freshwater marsh,
urban/developed, nursery, and turf.
Rationale
Core Habitat
Western pond turtles occur in permanent and semi-permanent aquatic habitats
from sea level to elevations of 1,980 meters (6,500 feet). They are found in
rivers, streams, lakes, ponds, wetlands, reservoirs, and brackish estuarine waters.
(Holland 1994; Jennings and Hayes 1994.) Western pond turtles use aquatic
habitats primarily for foraging, thermoregulation, and avoidance of predators.
Gravid females oviposit in sunny upland habitats, including grazed pastures.
Nesting has been reported to occur up to 402 meters (1,391 feet) from water
(Jennings and Hayes 1994), but is usually closer, averaging 28 meters (92 feet)
from aquatic habitat (Rathbun et al. 2002).
Movement and Overwintering Habitat
Pond turtles overwinter in both aquatic and terrestrial habitats. Terrestrial
overwintering habitat consists of burrows in leaf litter or soil. In woodland and
sage scrub habitats along coastal streams in central California, most pond turtles
leave the drying creeks in late summer and return after winter floods. These
turtles spend an average of 111 days at upland refuges that are an average of 50
meters (164 feet) from the creeks (Rathbun et al. 2002). Most hatchlings
overwinter in the nest and move to water in March and April, although some
leave the nest in September (Holland 1985a, 1991a, 1991b).
Model Results
Within the entire study area there are 1,470 acres of modeled aquatic and nesting
habitat and 6,406 acres of modeled movement and overwintering habitat for this
species.
Results of the habitat distribution model are based on two tiers of analysis. The
first tier of analysis is based on application of the assumptions provided above
using geographic information systems (GIS). Using this analysis none of the
ponds within the HCP study area were found to be unsuitable breeding habitat for
the western pond turtle. Thus all ponds in the HCP study area were considered
suitable breeding habitat and subject to the second tier of analysis. The second
tier of analysis involved application of data derived from field surveys of
68 ponds within the study area.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
6
REPTILES
Western Pond Turtle (Actinemys marmorata)
Biologists conducted the pond survey in September 2003. The purpose of this
survey was to provide both physical and biological data to assess and rank each
surveyed pond for breeding habitat suitability. Of the surveyed ponds, 28% were
considered unsuitable habitat because they did not contain water. Suitable ponds
were then ranked as having high suitability (given a score of 2) or low suitability
(given a score of 1) depending on the presence of basking sites and amount of
vegetation present. Based on this characteristic, 29 % of the ponds were
considered highly suitable breeding habitat while 43% of the ponds were
considered moderately suitable breeding habitat (Figure 2).
The final step in the second tier of analysis was to extrapolate the findings from
the pond survey (68 pond sample) to all ponds in the study area considered
suitable after the first tier of analysis. The goal of the extrapolation is to
determine the acres of suitable pond breeding habitat in the study area based on
the results of our pond survey. For the western pond turtle, our analysis indicates
that 72% of the surveyed ponds contain suitable breeding habitat. (For the
extrapolation, all ponds receiving a score of 1 or 2 were considered suitable
breeding habitat.) Finally, in order to ensure that the results of our surveys
represent a conservative estimate of suitable habitat, we increased the total
percent of suitable pond habitat derived from this analysis by 10%. The result of
this multi-tiered analysis is a total of 1,470 acres of modeled aquatic and nesting
habitat comprised of 33 acres of pond habitat and 1,437 acres of perennial
stream, reservoir, and adjacent nesting habitat.
Species Profiles
SFPUC Alameda Watershed Habitat Conservation Plan
November 2011
7
Species Range
HCP Study Area
Year-round Range
0
100
MILES
FIGURE 1
Western Pond Turtle (Clemmys marmorata)
Distribution
Source: Stebbins 1985 and CWHR 2001
Figure 2 Habitat Distribution Model for Northwestern Pond Turtle (Clemmys marmorata marmorata)
Legend
d
thi
ll
te
ou
V all
!
(
!
(
!
(
Vallec ito
ed
m
se
r
!
(
!
( !
(
!
(
Pond Habitat Suitability = Moderate
!
(
Pond Habitat Suitability = Not Suitable
Suitable Movement and Overwintering Habitat
!
(
!
((
! !
(
!
(
!
(
!
(
!
( !
(
ek
!
(
!
(
!
(
!
(!
(
(!
!
(
o
Stream
k
ee
e !(
rs
Cr
Cre e k
Known Occurrence
(Denotes one occurrence
within polygon)
!
(
!
(
p
Core (Includes Nesting) Habitat
ian
s
ne
Hay h
Gulc
lch
!
(
!
(
d
In
d
oa
n R
We
!
(
!
(
!
(
Cre
!
( !
(
A!(!(!(
p
!
(
h
!
(
!
(
s
lc
!
(
!
(
m
!
(
!
(
!
(
!
(
ia
!
(
!
(
(
!
(!
!
(
!
(
!
(
!
(
!
(
!
(
!
(
ill
!
(!
(
u
!
(
!
(
!
(
!
(
!
(
G
!
(
W
ek
Unsurveyed pond
(Note: Core Breeding Habitat in
ponds cannot be seen at
this scale, and are overwritten
by Pond Habitat Suitablity points.)
!
(
!
(
!
(
!
(
(
!!
(
!
(
a
os t
ida
She r
Fremont
!
(
!
(
Va
l le
!
(
!
(
Cr
e
!
(
!
(
!
(
!
(
!
(
!
(
!
(
!
(
!
(
!
(
!
(
!
(
!
(
n A
C
La
!
(
i
to n
Sa
!
!
( (
!
(!
(
!
(
!
(
!
(
An
Sa n
!
(
d
s Roa
I
alavera
0
68
Pond Habitat Suitability = High
Unsurveyed Ponds
De
l
!
(
!
(
o
!
(
!
(
ni
!
(
ir
vo
nt o
!
(
C
y
lle
Va
nol
-
!
(
e ek
!
(
!
(!
(
!
((
!!
(
!
(
(
!
(!
( !
!
(!
(
!
(
!
(
!
(
k
Su
!
(
ree
!
(
Re
!
( !
(
's C
!
(
a
Cr
!
(
s R
!
(
/ R
!
(
!
(
!
(
(!
(
!
(!
o
ecit
d
oa
o
Al a
Foo
le
s
Ni
Sunol
ad
Surveyed Ponds
84
ke
La
Ro
a
d e la L a gun
Cany on
R
80
o
roy
I-6
Ar
n
!
(
R
g
ee
Study Area
SFPUC Ownership
e
Cr
Secondary Road
County Line
id
L
n
Reservoir
!
(
!
(
!
(
de
ey
Primary Road
k
!
(
(!
!
(
!
(
!
(
A lame
d a Cr
ee
k
(
!!
(
!
(
!
(
Oa
!
(
!
(
Ca
la
I - 6 80
We
lle r
0
I-88
ve
Re
R oa d
!
(
se
rvo
ir
Santa Clara Co.
!
(
P
!
(
!
(
o
ve
rt
!
(
!
(
!
(
y
0
!
(
Ho
d
oa
Ma r s
nd
o
R
!
(
g
as
e
er
Calav
ee
Cr
!
(
!
(
!
(
!
(
!
(
k
Mt.
Day
!
(
5/5/08
!
(
1
1:100,080
!
(
!
(
0.5
2
Miles
!
(
id
!
(
©
Alameda Co.
!
(
!
(
!
(
h R
d g !(
!
( e
o
roy
Ar
as R o ad
er
Felt
!
(
!
(
!
(
Cal a ve r
Milpitas
Ri
ra s
!
(
d
Roa
k