Behavioral Responses of Elk to Predation by Wolves: Physiological Costs and Dynamical Consequences

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Most theoretical models of the impact that predators have on prey populations focus exclusively on direct offtake and its impact on the survival rate of prey. However, most prey species modify their behavior when predators are present, to reduce the risk of predation. Because these behavioral responses require time and energy, they are likely to affect the survival and reproduction of prey species in ways that should be incorporated into predator-prey models. This research will examine the behavioral responses of elk to the risk of predation by wolves, in three ways. (1) Most fundamentally, it will test for behavioral responses of elk to spatial and temporal variation in the risk of predation by wolves. The behavioral responses to be examined include patterns of herding, individual time budgets, movement patterns, spatial distributions, and habitat selection. (2) It will then test for physiological costs associated with antipredator responses, using fecal glucocorticoids to measure stress, snow-urine allantoin:creatinine ratios to measure foraging success, and fecal progestins to measure pregnancy rates. (3) Finally, it will determine the impacts of antipredator behavior on patterns of survival and changes in population size. The reintroduction of wolves to the Greater Yellowstone Ecosystem has produced a rapidly growing and geographically expanding population. The steady growth and expansion of wolves has generated enormous controversy among wildlife managers, conservation biologists, state and federal lawmakers, the media, and the general public. Sitting at the heart of this controversy is the potential impact of wolf predation on wildlife populations, particularly elk. This research will produce substantial data on rates of wolf predation and its effects on elk demography, distribution and dynamics. These data will play a critical role in establishing policies for the management of wolves and elk.