Beyond 2000 Symposium

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Wolf - Prey Interactions

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Beyond 2000:
Realities of Global Wolf Restoration

23-26 February 2000
Duluth, Minnesota USA

Spatial and temporal variability of Yellowstone's northern range elk (Cervus elaphus) herd in wolf (Canis lupus) pack territories

Carrie L. Schaefer, Rolf O. Peterson, School of Forestry and Wood Products, Michigan Technological University, Houghton, MI 49931, USA; Douglas W. Smith, Kerry M. Murphy, Yellowstone Center for Resources, PO Box 621, Yellowstone National Park, WY 82190, USA

Elk are the most abundant ungulate species in Yellowstone National Park (YNP). The northern Yellowstone elk herd is the largest migratory herd and winters along low elevation river drainages referred to as the northern range. Since the late 1960's, park managers adopted a natural regulation policy that called for the regulation of ungulates without human interference. Observing elk numbers and the potential effects on their winter range has prompted much study of this ecosystem.

From 1935-1995 YNP lacked a significant predator, the gray wolf, which managers restored in 1995 and 1996. With the restoration of wolves on the northern range, many questions have been raised regarding the wolves' effect on the prey base, particularly elk. Many studies have documented the impacts of wolf predation in single and multiple ungulate systems, but none involving the reintroduction of a major predator.

Spatial and temporal variation in the northern range elk herd was estimated by surveying elk during early and late winter. Elk were counted and classified from the ground in predetermined areas encompassing the elevational gradient along the northern range, and from the air in northern range wolf pack territories. Evaluating the effectiveness of these two methodologies is important for long-term study wolf and elk dynamics on the northern range. Comparison of simultaneous ground observers' counts and classification is important in determining observer variability, elk group size, age and sex classification, time of year and location along the northern range.

To test the hypothesis that wolf predation plays a nonessential role in the regulation of the elk population, elk density in wolf pack territories was compared to kill rates and kill composition to determine if a traditional functional response exists. Densities of elk in wolf pack territories during early winter ranged from 0.3 - 18.48 elk/km2 and during late winter ranged from 0.1 - 6.65 elk/km2. Estimating calf:cow and bull:cow ratios across the northern range and over time can provide a population index for this herd and will contribute to the long-term documentation of population trends. Calf:cow ratios during early winter ranged from 3 - 28 calves/100 cows from ground observations and 0 - 10 calves/100 cows from aerial surveys. Calf:cow ratios during late winter ranged from 0 - 23 calves/100 cows from ground observations and 0 - 13 calves/100 cows from aerial surveys. Documenting the responses of elk population parameters to wolf recovery will provide insight into clarifying the role of predation on the northern range.