Download WESTERN SCREECH OWL

Species Natural History Project
Diana Molina LA 541 10.21.10
Part 1: Species Natural History Account
OWL LIFE CYCLE
WESTERN SCREECH OWL
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A young Western Screech Owl talks with Santa. 3
Family: Strigidae
Scientific Name: Megascops kennicotti (formerly Otus kennicotti)
Common Name: Western Screech Owl (Little Horned Owl, Dusk Owl, Ghost Owl, Mouse Owl, Cat
Owl, Little Cat Owl, Puget Sound Screech Owl, Washington Screech Owl, and Coastal Screech Owl)
1. STAGE 1: NEST
No nest material is added and nests are kept clean. 2-5 eggs are laid on natural
sawdust on the floor of tree cavities. Eggs are laid every 1 to 2 days and the incubation
period lasts 26 days on average. Females incubate brood while males bring food to the
nest.1
2. STAGE 2: FLEDGLING
4-5 week stage. During this stage, owls like to climb on tree snags and branches.
Fledglings are lighter in coloring but more patterned than adult owls.2
3. STAGE 3: YOUNG ADULT
Young adults disperse from natal area on average 58 days post-fledgling,
predominantly during the autumn months.1
4. STAGE 4: ADULT – 1-20 YEARS
Western Screech owls nest almost exclusively in tree cavities.1 They require cavities
from trees with a Dbh of at least 12 inches.5 Nest cavities are at least 20 feet from the
ground and up to 50 feet. Nests are almost always in deciduous trees. Pairs will often
reuse nest sites in consecutive years and will mate for life. Adults tend to remain near
breeding areas and aggressively defend their nests.1,2
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A. Preferred Local Habitats:
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breeding season very little overlap occurred within pairs. We did not detect overlap
between neighboring pairs.!" !
Riparian Forest/Woodland: Hunting and habitat areas.
Wet Prairie: Hunting areas6
Oak-Pine Woodland: Thought to breed where oaks occur.
Western Screech owls are dependent on deciduous woodlands or open mixed forests
that have suitable nesting sites and sufficient prey densities. Densities are highest in
riparian zones.1
Spatial and Landscape Data:
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B. Life History & Description:
Home range: 3-9 hectares (8-22 acres). Home ranges of Western Screech-owls were
highly associated with riparian forests; most screech owls had ≥10 ha (25 acres) of
riparian-forested habitats within their home ranges#!" !
!
Territory size: Moderately widespread. (See Figure 1). Elevation range 500-4000 ft.
Figure 2 1
Life Cycle Stages and Life Span:
• Age at cessation of parental care: Fledge at 4-5 weeks. Disperse from natal area on
average 58 days post-fledging. 1
• Life span: 12 years on average and 20 years maximum.2
• Appearance: Juveniles have a more intricately variegated plumage with many
feathers tipped with white. Adults in the southwest are paler grey, while birds in the
northwest are darker and browner. A cinnamon coloring is rare and found only in the
Pacific Northwest.1
• Habits: Predominantly nocturnal with activity beginning 20-30 minutes after sunset.
Very territorial and aggressive when defending a nest site. May attack humans.1
Hunts mainly from a perch in open woodlands, along the edges of open fields, or
wetlands, or makes short forays into open fields. They also capture insects while
in flight.1
Size:
• Female: Avg. length : 23cm (9.2”) Wingspan 56cm (22”)1
• Male: Avg. length: 21cm (8.2”) Wingspan 54cm (21”)1
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Weights of different subspecies vary widely. In general weights decrease for owls
found in southern areas. “An average of 186g (6.5 oz) for females and 152g (5.3 oz) for
males in a northern population to 123g (4.3oz) and 111g (3.9oz) for females and males
in southern populations, respectively.2
Reproduction and Population Data:2
• Age at first breeding: 1 year
• Breeding areas: Nests in natural cavities, woodpecker holes (Flicker and Pileated) and
in nest boxes.
• Offspring per litter (eggs per clutch): 2-4
• Litters per year: 1
Seasonal Activity and Movements:
• Breeding period: March to August
• Migration: Owls occur all year and are not known to migrate. Altitudinal migration is
speculated.!
• Distance between natal and breeding area:!Unknown"!!During the breeding season,
males and females of a single pair overlapped extensively, whereas outside the
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Population and meta-population needs: Because breeding owls will often reuse
nest sites in consecutive years and pairs mate for life, preservation of habitat over the
long-term (stability) is key to owl survival. Further, adults tend to remain near their
breeding areas year-round and defend nest sites vigorously.1
Due to the lack of migration and significant population movement new habitats must
be connected to existing habitats through natural corridors and allocated to ensure
minimal overlap between breeding pairs.
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Diet and foraging locations: Varied diet includes voles, deer mice, shrews, harvest
mice, kangaroo rats, pocket gophers and bats. Preferred bird prey includes house
sparrows and starlings. Preferred amphibian prey: lizards, salamanders, frogs, and
small fish. Insect prey includes beetles, cicadas, ants, grasshoppers, worms and
centipedes.2
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Range of environmental tolerances: Owls will avoid densely forested areas, such as
old growth coniferous forests that are home to Great Horned Owls, which are
predators.4
Owl/human relationship: Although this owl is known to aggressively defend its territory, it
can survive in wooded suburban areas and city parks as long as it is not directly
persecuted or disturbed by humans.1
E. Willamette Valley Habitats and Species Status:
Which are the most important Willamette valley habitat types for this species?
Cavities for nesting and roosting in trees with a minimum dbh of 12 inches. Strongest Oregon
habitat association in Douglas Fir-White Oak Forest and Western Oregon riverine woodland.5
Humid Douglas-fir, western hemlock, western red cedar, and Sitka spruce forests along the
edges of clearings, rivers, and lakes are the preferred Willamette valley habitat types for the
Western Screech owl. 1 Of secondary importance is open Oak savanna areas where the owl is
thought to hunt.2
C. Habitat Elements and Processes:
Are there specific habitat elements necessary to this species, and in what ways are they
used? Are there key ecological processes that these species rely on for establishment,
persistence, or reproduction?
Does it require interior or edge conditions? The Western Screech owl is an edge condition
species, as it relies on open areas to hunt and mixed-deciduous/coniferous forests for shelter.
Western Screech owls thrive in edge habitats that are made up of mixed deciduous forest to
nest in, riparian forest to nest and hunt and open Oak savanna (also to hunt). Of paramount
importance are tree cavities in dead and dying trees that are required for nesting and tree
snags and leaning trees that juvenile owls like to climb. 1,2
What is the species status in the Willamette Valley? Although the Western Screech owl is
not endangered, they are difficult to survey because of their secretive nature.!$
These owls rely on natural forest vegetation succession cycles and use gaps in the forest,
caused by natural disturbance regimes, as primary hunting areas. Areas of old growth
provide suitable habitat and nesting sites, while areas of young growth provide open space to
facilitate spotting prey.
Is it known to be declining or decreasing? The meta-population is not under threat due
to its wide range along the western coast of the U.S. into Canada and Mexico. However
populations are decreasing due to increasing urbanization and silviculture practices that
reduce the number of available tree cavities and rotting trees used for nesting.
What are the key threats this species faces or is likely to face in Eugene and the
surrounding environment? A limiting factor in their numbers is the available of suitable nest
cavities. Urban development is a threat to habitat, although these owls will breed in suburbs
and city parks with established trees.2
D. Key Ecological Functions:
What is the species role in the ecosystem, food web, and relationships with other
species?
The Washington Breeding Bird Survey has recorded a decline in numbers in recent years
throughout the species' range, and declines have also been observed in southern British
Columbia. There is speculation that predation from the expanding population of Barred Owls,
recent arrivals in some areas, is a factor.1
The Western Screech Owl is a heterotrophic consumer and primary predator (or primary
carnivore). It consumes terrestrial vertebrates and invertebrates that are often secondary
consumers. It also preys on primary consumers such as flying insects and worms.
They can fall prey to Northern Goshawks, Cooper’s Hawks and Great Horned, Barred, Spotted,
and Long-eared Owls, all of which are larger in size than the Western Screech Owl.1
Other predators include weasels, raccoons, snakes and crows.1
Owls depend on woodpeckers that create tree cavities in which to nest. Specifically, the
Flickered and Pileated woodpeckers.2
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GENERAL GUIDELINES AND RECOMMENDATIONS
Home range and territory size: 7.5 to 150 acres, with territories as close as 165 feet
apart.1
Recommended number of cavities or snags or volumes of large downed wood
per unit area:
Western Screech Owls Vary in appearance.5
Part 2: Design, Planning and Management Guide
Because Western Screech Owls usually reuse nesting sites, it is more crucial to provide
large habitat patches that contain mature deciduous forests than to focus on
General guidelines and recommendations
Diagram 1: Residential House/Yard Scale
Diagram 2: Urban Park Scale
Diagram 3: Urban Open Space System (Larger scale)
providing a specific number of cavities or snags. That said, it is a good idea to provide
a variety of cavities at heights between 20-50 feet that are near riparian zones, where
owls like to feed.
How could your design recommendations be strengthened by specific aesthetic
approaches to make them a desirable part of the urban fabric, especially if those
recommendations are not part of common landscape practices or aesthetics?
What critical knowledge gaps might exist for this species?
Western Screech Owls thrive in lands containing a variety of vegetative species but
which are generally not densely covered. This makes suburban and residential forest
areas suitable habitat provided that water sources and larger habitat patches are
nearby. Fortunately, humans also prefer open turf, deciduous trees, and water
features in their own habitat, so there is great potential for transforming the urban
landscape into a more owl-friendly environment.
However, owls require the use of dying and decaying trees and snags, both as nesting
ground and a source of food for their prey. Wetland or water areas that contain
rotting tree trunks, rocks and a good mix of shrub and canopy layer attract a variety of
species on which the owls feed. While it is difficult to convince human residents to let
go of their manicured, English garden aesthetic, applying a combination of open
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neatly trimmed lawn (native grasses) and wet, brushy, and naturalistic areas can help
to maintain a sense of order while also providing owls with the variety of spaces they
DIAGRAM 1: RESIDENTIAL HOUSE AND YARD
need to survive.
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Further, since owl territories are generally much larger than the typical residential lot,
designing effective owl habitat requires cooperation at the neighborhood scale. If
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neighbors agree to create a more unified habitat collectively, they will be more
accepting of more “radical” design solutions if they see their neighbors doing the
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same.
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The following diagrams make suggestions for improving the urban fabric for owls at
three different scales: residential, urban park, and city. Little is known about the
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distance between natal area and breeding sites.2 This information would be of great
use when designing suitable habitat, as provision of sufficient nesting sites could be
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anticipated and provided if more was known about population behavior.
30-50 Ft. (Avg. residential lot width)
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1. Preserving and protecting large tree species on site is essential for providing owl
habitat. Trees should be at least 12”dbh to serve as nesting areas.
2. Providing a mix of deciduous (large trees) and evergreen shrubs ensures that
there is vegetation year round. This provides suitable prey hiding areas and
helps to soften the edge of built structures, which can disrupt
vegetation/habitat corridors.
3. Addition of features such as green roofs can provide foraging areas for small
prey (rodents, insects etc). and double as an “open savanna-like” feeding area.
Owls can hunt here while perched on tall trees.
4. Eliminating or reducing fences allows owl prey to move more freely between
residential lots and between residential lots and denser forested habitat.
5. Mixing old established trees with younger trees provides a canopy height
variety from which owls can perch undetected while slowly approaching prey.
6. Water features such as ponds and swales provide excellent amphibian and small
rodent habitat, especially if they remain wet year round.
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7. Western Screech owls favor riparian trees such as poplars and ashes. Planting
trees near water allows the owls to hunt more effectively from a perched
position.
8. Downed wood and rotting wood can become an excellent insect habitat and
draw small birds into the area. Owls feed on both insects and smaller birds.
Keeping a discrete edge between the naturalistic water area and a neat and trim
lawn helps to maintain a sense of order while also providing the necessary
“messiness” that comes with allowing rotting and decomposing elements to
remain in the landscape.
9. Native grasses can take the place of chemically treated lawn. These grasses
must be allowed to yellow and dry in the winter, when food is scarcer for owls.
The remaining wetness of the water feature thus becomes a magnet for owl
prey since it will act as a magnet for remaining prey.
DIAGRAM 2: URBAN PARK
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2. Whenever possible, large trees or large patches of mature forest should be
preserved or established.
3. Water features should occur near forested areas. Although creeks or streams are
preferable, ponds can also provide suitable frog and insect habitat. Edges of
water features should be more naturalistic in appearance. Retaining walls and
cement edges are prohibitive for migrating and terrestrially bound owl prey.
Ponds or streams should have a shallow pool edge, as small birds enjoy bathing
and feeding in these areas. By maintaining an open edge, owls are given more
visibility to hunt prey from a perched position.
4. Human activity areas should be buffered by low vegetation on at least one side.
This allows a degree of separation between owl nesting habitat and humans.
Owls are aggressive defenders of their nests and prefer humans at a distance.
5. Paths should make up a small percentage of park space and not bisect open
areas whenever possible.
6. A mix of treed and open areas is ideal for both owls and humans.
7. Younger trees or taller shrub layers can provide a variety of heights from which
owls can perch. This is also more aesthetically pleasing to humans.
8. Adjacent building setbacks should be increased for new construction to allow
space for planting deciduous street trees. Enough space for trees to mature is
preferable to connect owl habitat corridors.
9. Some use of evergreen trees is also necessary to provide hiding areas for owls
year round.
10. Roofs of large structures could be planted to connect green corridors in the
urban environment.
11. Car traffic should be slowed down as much as possible. Eliminating fast, wide
streets and pass-through traffic will help create a calmer environment more
suitable for Western Screech owls, especially because they roost during the
active urban daytime hours.
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200 Ft.
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1. Planting street trees along edges of parks and in between built structures helps
to maintain a more connected habitat corridor for owls and for their prey.
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DIAGRAM 3: URBAN OPEN SPACE SYSTEM
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4. Because owls need at least 7 acres per breeding pair, urban residential grid areas
can be planted with deciduous trees and owl habitats fashioned at the
neighborhood scale.
#" Existing large, forest habitat near urban areas should be preserved, especially
around the edges between denser forest and open space. This makes ideal
Western Screech owl habitat.!
$" Large areas of impervious cover and lack of trees are least suitable owl feeding
and nesting habitat and should be mitigated by the use of street trees, green
streets, and water features.!
%"Denotes highway.!
&" Low-density development is suitable for owls, particularly when it occurs near
undeveloped forest. These neighborhoods tend to have more canopy cover,
and house a variety of rodent and insect species upon which owls feed.!
'" Every effort to connect existing open space should be made to improve habitat
for a variety of species, not just owls.!
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1 mile
1. Unimproved pasture areas might provide alternative feeding and breeding
areas for owls, especially in shelterbelts, hedgerows with trees and adjacent
remnant woodlots.
2. Riparian areas should be restored where not vegetated. Owls prefer poplars,
ashes, alders, and even willows, especially near water. Dense urban
development, channelized streams or rivers, and too much impervious cover
can significantly reduce owl habitat.
3. Industrial areas can be planted, and impervious cover reduced to provide
habitat corridor. While owls are not likely to breed or nest in these areas, large
industrial zones can help owl prey connect from denser forest to riparian zones
that are often areas of industry.
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Resources/Works Cited:
1. Owl Pages. < http://www.owlpages.com/owls.php?genus=Megascops&species=kennicottii>
2. Wildlife Habitats CD. Northwest Habitat Institute. Query: Western Screech Owl.
4. Seattle Audobon. <http://www.seattleaudubon.org/birdweb/bird_details.aspx?id=242>
5. US Forest Service : Deschutes & Ochoco National Forests Crooked River National Grassland
<http://www.fs.fed.us/r6/centraloregon/wildlife/species/birds/birdsofprey-owls.shtml>
6. Davis, Helen and Weir, Richard D. “Home Ranges and Spatial Organization of Western
Screech-Owls in Southern British Columbia” Northwestern Naturalist 91(2):157-164. 2010.
Published November 10, 2009.
Photo Credits in order of appearance:
1. Little Pearls, “Wild and Free: A Screech Owl Named Pinkey”. <www.littlepearls.org >
2. US Forest Service : Deschutes & Ochoco National Forests Crooked River National
Grassland <http://www.fs.fed.us/r6/centraloregon/wildlife/species/birds/birdsofpreyowls.shtml>
3. Widescreen Wallpapers. <www.widescreenwallpapers.com>
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Diana Molina
Principles of Applied Ecology