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FORAGING ECOLOGY, VIGILANCE OF COYOTES,
AND “BEHAVIORAL CASCADES” IN RESPONSE
TO GRAY WOLF REINTRODUCTION IN
YELLOWSTONE NATIONAL PARK
T. Adam Switalski
Post-Project Seminar
December 11, 2001
Introduction
• Species loss:
– Carnivores particularly at risk:
• Inherent rarity
• Large habitat requirements
• Competition with humans
Introduction
• Extirpation of Keystone Predators leads to:
– Disturbed unstable systems
• Increased numbers of prey and competing carnivores
• Expanded range
• Loss of anti-predatory behaviors
– Vigilance
– Avoidance
• Ultimately, cascading effects
Wolf Range: Past, Present, and Future
Introduction
• Case study: reintroduction of wolves in
Yellowstone National Park
• How are coyotes learning to coexist with wolves?
• How are other species responding numerically and
behaviorally?
– What are the cascading effects?
Foraging Ecology and Vigilance of
Coyotes in Response to Wolf
Reintroduction
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Introduction
Study area
Methods
Results
Discussion
Coyote and Wolf Coexistence
• No coexistence
• Resource partitioning
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Spatial avoidance
Temporal separation
Low degree of diet overlap
Different habitat use
Return of the Wolf to YNP
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Historical coexistence
1995, wolves translocated from Canada
Designated “nonessential experimental” population
Population increased quickly with highest fecundity
recorded for species
Foraging Ecology and Vigilance:
Research Questions
Foraging Ecology and Vigilance:
Research Questions
• Do coyotes exhibit different behavioral
time budgets now as compared to before
wolves were reintroduced into YNP?
Foraging Ecology and Vigilance:
Research Questions
• Do coyotes exhibit different behavioral
time budgets now as compared to before
wolves were reintroduced into YNP?
• Do coyotes living between wolf packs
(‘buffer zones’) exhibit different behavioral
time budgets than coyotes in high wolf use
areas?
Foraging Ecology and Vigilance:
Research Questions
• Now that wolves have become established
in the Lamar Valley, do coyotes exhibit
different behavioral time budgets when
wolves are physically present as opposed
to their absence?
Study Area: Lamar Valley
Food Resources
Methods
• Observations of coyotes and wolves from
winter 1998 to summer 2000
Methods
• Recorded:
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Wolf and coyote location
Type of behavior and time of day
Travel route
Location of behavior
Sex
Social status
Age class
Pack
Pack size
Coyote Behaviors
• Rest (alert, sleep)
• Travel
• Hunting small mammals
• Feeding on carcass
• Vigilance
• Howling
• Other
Small Mammal Surveys
• Captured during summer 1999 and 2000
• 3 different sites for 2 sessions each year
• Mini-grids trapped for 4 days 5 nights and
checked twice daily
• Once identified, the small mammals were:
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Toenail clipped
Weighed
Sexed
Released
Statistics
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SAS
Factorial (split-plot) design
Analysis of variance using PROC MIXED
Snow depth was repeated measure
Sample unit was the individual coyote
Proportion of time
Each observation was given equal weight
Statistics
• Variables analyzed included:
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Wolf activity
Wolf presence
Sex
Year
Results
• From December 1997 to July 2000 we made:
– 1243 observations of coyotes
– 1743 h of coyote activity budgets
• 28 resident coyotes from 9 packs
• 16 male and 12 females
• 24 alphas and 4 betas
Lamar Valley Coyotes
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For 60 years, coyotes thrived without wolves
Coyote population reduced 25 to 33% each winter
23 observed coyote mortalities
Average pack size 3.2 (range = 2.7-3.7)
Very low recruitment (predation and parvo)
Lamar Valley Wolves
• Druid Peak and Rose Creek packs introduced
into Lamar Valley in 1995 and 1996
• Pack sizes:
• 7-8 adults in Druid Peak
• 15-22 adults in Rose Creek
• Druid Peak pack denned within study area
• Wolf territories overlapped creating “buffer zone”
Coyote and Wolf Pack Territories
Including Wolf “Buffer Zone”
Mean Snow Depth
60
1998
SNOW DEPTH (cm)
50
1999
2000
40
30
20
10
0
N
N
D
D
J
J
F
MONTH
F
M
M
A
Coyote Behavioral Time Budgets
Before and After Reintroduction
PROPORTION OF TIME
0.6
0.5
PRE-WOLF
0.4
POST-WOLF
0.3
0.2
0.1
0
BEHAVIOR
Coyote Behavioral Time Budgets
REST
TRAVEL
HUNT
CARCASS
VIGILANCE
PROPORTION
OF TIME
1
0.8
0.6
0.4
0.2
0
D
J
F
M
MONTH
A
M
J
Coyote Behavioral Time Budgets
REST
TRAVEL
HUNT
CARCASS
VIGILANCE
PROPORTION
OF TIME
1
0.8
0.6
0.4
0.2
0
D
J
F
M
MONTH
A
M
J
Coyote Behavioral Time Budgets
REST
TRAVEL
HUNT
CARCASS
VIGILANCE
PROPORTION
OF TIME
1
0.8
0.6
0.4
0.2
0
D
J
F
M
MONTH
A
M
J
Coyote Behavioral Time Budgets
REST
TRAVEL
HUNT
CARCASS
VIGILANCE
PROPORTION
OF TIME
1
0.8
0.6
0.4
0.2
0
D
J
F
M
MONTH
A
M
J
Coyote Behavioral Time Budgets
REST
TRAVEL
HUNT
CARCASS
VIGILANCE
PROPORTION
OF TIME
1
0.8
0.6
0.4
0.2
0
D
J
F
M
MONTH
A
M
J
Coyote Behavioral Time Budgets
REST
TRAVEL
HUNT
CARCASS
VIGILANCE
PROPORTION
OF TIME
1
0.8
0.6
0.4
0.2
0
D
J
F
M
MONTH
A
M
J
PROPORTION OF TIME
Different Levels of Wolf Activity
0.6
0.5
BUFFER
0.4
NONBUFFER
0.3
0.2
0.1
0
REST
CARCASS
BEHAVIOR
VIGILANCE
PROPORTION OF TIME
Presence and Absence of Wolves
0.6
0.5
ABSENT
0.4
PRESENT
0.3
0.2
0.1
0
REST
CARCASS
BEHAVIOR
VIGILANCE
Discussion
• In response to wolf reintroduction
coyotes have adjusted their behavior:
– Spatially (buffer zone vs. non-buffer zone)
– Temporally (present vs. absent)
How has coyote behavior changed?
• Increase in the amount of time feeding on
carcasses
• Consistent with wolf recolonization in NW Montana
(Arjo and Pletscher 1999)
• Feeding on carcasses throughout the year
• Contrasts Gese et al. (1996)
• Decrease in travel
Energetic Benefits
• Wild coyotes need 930 g of food daily
(Bekoff and Wells 1986)
– Coyote must consume the equivalent of:
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27 mice
11 microtines
6 pocket gophers
4 ground squirrels
– or
• Risking a few minutes feeding on a wolf-killed carcass
How is behavior different in
the “buffer zone?”
• Wolf buffer zones:
– Higher deer survivorship
– Refuge for coyotes
– In YNP, coyotes between Rose Creek and
Druid Peak wolf packs have:
• Fewer agonistic interactions
• Lower mortality rates
• Different behaviors
How is behavior different in
the “buffer zone?”
• Coyote behavior in the buffer zone:
– Fed on carcasses less
• Little wolf-killed carrion available
– Rested more
– Vigilant less
• Less wary of predation by wolves
Is Behavior Different Wolf Presence?
• When wolves were present:
– Fed on carcasses more
• Wolf-killed carrion almost always present
– Rested less
– Vigilant more
• More wary of predation by wolves
• Most coyotes were killed while scavenging wolf kills
Coyote Behavior - Conclusion
• Coyote population reduced
• Surviving coyotes adjusted behavior
– Coyotes benefit from wolf-killed carcasses
• Increased feeding on carcasses
– Increased costs:
• Increased vigilance
• Decreased rest
• Higher predation risk
– Impact varies spatially and temporally
What is the big picture?
• Reintroduction of large carnivores leads to:
– Numeric response
– Behavioral response
• Cascading effects
Numeric Response to
Reintroductions
Numeric Response to
Reintroductions
• Contrary results in prey species
– In NW MT, elk and deer populations decreased
– No prey reduction in YNP, MN, and WI
• Reduction of competing carnivores
– Coyote population reduced in NW MT and YNP
Behavioral Response to
Reintroduction
• Minimize encounters
– Adjust spatial and/or temporal use:
• Elk in National Elk Refuge dispersed
• Coyotes in NW MT avoided wolves
• Decrease success of attacking predator
– Increased vigilance
Vigilance
• Aids in:
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Detection of predators
Observation of conspecifics
Food acquisition
Prevention of kleptoparasitism
Environmental and Social Variables
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Group size
Distance to refuge
Position in the herd
Body size
Age
Parenthood
Habitat type
Predation pressure
Ecotourism
Vigilance Conclusions
• Increased risk of predation results in
increase in vigilance
• Increase in vigilance increases the animals
safety, however decreases foraging
• In GYE since wolf reintroduction:
– Elk, moose, and coyotes have increased
their vigilance
Cascading Effects
• In YNP, reduction of elk population:
– Allow vegetation to recover
– Increase population of competing herbivores
• On Isle Royale, increase in wolf
population resulted in:
– Decrease of moose population
– Recovery of balsam fir
“Behavioral Cascades”
• IN YNP, No reduction of elk population,
however behavior changes:
– Avoiding high wolf use areas
• Aspen and willow recovery
– Higher diversity of song birds
– Increased number of spotted frogs
– Recolonization of beaver
“Behavioral Cascades”
• In YNP, decrease in coyote population
and behavior changes:
– Increase of feeding on carcasses
– Avoidance of high wolf use areas
• Increase in small mammal density
• Increase in the number of badgers, weasels, and
foxes
“Behavioral Cascades”: the
Numeric and Behavioral Dichotomy
• Behavior changes may reduce fitness
– Increased vigilance in elk may result in:
• Reduced fat content and lower body mass in females
• Lower survival rates during the winter
• Calves born with lower weights
– Increased vigilance in coyotes may result in:
• Reduced survival of pups
Conclusion
• Reintroduction of wolves has lead to:
– Reduction of prey populations???
– Reduction of competing carnivore population
– Change in behavior
• Increase in anti-predatory behaviors (vigilance)
• Change in space use
– Ultimately, cascading effects may lead to an
increase in biodiversity
Acknowledgements
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Major Advisor: John Bissonette
Eric Gese, Jim MacMahon, and Bill Adair
Susan Durham for statistical consultation
Yellowstone Ecosystem Research Center
Friends and family