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 Introduction Study area Methods Results Discussion

Coyote and Wolf Coexistence No coexistence Resource partitioning –Spatial avoidance –Temporal separation –Low degree of diet overlap –Different habitat use

Return of the Wolf to YNP 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

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 : 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 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: Toenail clipped Weighed Sexed Released

Statistics 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: –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 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 = ) 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 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

Coyote Behavioral Time Budgets Before and After Reintroduction

Coyote Behavioral Time Budgets

Different Levels of Wolf Activity

Presence and Absence of Wolves

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: 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

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: –Detection of predators –Observation of conspecifics –Food acquisition –Prevention of kleptoparasitism

Environmental and Social Variables 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

Major Advisor: John Bissonette Eric Gese, Jim MacMahon, and Bill Adair Susan Durham for statistical consultation Yellowstone Ecosystem Research Center Friends and family Acknowledgements