Beyond 2000 Symposium

Program

Wolf - Prey Interactions

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Beyond 2000:
Realities of Global Wolf Restoration

23-26 February 2000
Duluth, Minnesota USA

Effects of elk herding on predation by gray wolves in Banff National Park, Alberta

Mark Hebblewhite, Daniel H. Pletscher, Wildlife Biology Program, University of Montana, Missoula, MT 59812, USA

Elk are social ungulates and are the main prey item in the diet of wolves in a complex multi-prey system in Banff National Park (BNP), Alberta. Predator-prey research has largely focused on single prey systems in North America dominated by Moose or White-tailed deer, and researchers have made significant advancements in both the theory and management of these systems. However, theoretical work and field studies where a predator preys on a social species suggest that herding behavior can influence predation. Herding can affect the functional response of predators by affecting the way predators encounter and kill prey, and this can have density independent or density dependent effects on population dynamics, dependent on the relationship between density and herd size.

We studied wolf predation on elk in BNP by two wolf packs during two winters from 1997 to 1999, and described how elk herding affected the availability, the encounter rates, and the killing rates of elk by wolves. Elk herd size availability was determined by aerial survey and ground sightings, and the size of encountered herds of elk and the herd size from which wolves made successful elk kills were estimated through ground snow-tracking and through coordination with a radio-collared elk study. Wolves encountered elk in different herd sizes according what was available, but had higher attack success in larger elk herds, killing more elk per encounter from larger elk herds. As elk density increases in BNP, herd size also increases. The combination of higher attack success in larger herds and this herd size-density relationship could create conditions where elk herding by itself causes wolf predation to be density-dependent. We developed an individual elk predation risk model to examine whether individual elk still gain benefit from herding under this predation regime. We found that elk may be making the best of a bad situation in evolutionary ecology terms by minimizing individual risk through a strategy that increases predation on elk at high densities. This research has broad implications for predator-prey management in systems where the main food item of wolves is elk.