1. Department of Wildlife Ecology, University of Wisconsin, Madison, Wisconsin 53706, USA
2. Present address: Denver Wildlife Research Center, Department of Fisheries and Wildlife, Utah State University, Logan, Utah 84322-5295, USA
3. Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin, Madison, Wisconsin 53706, USA
4. Yellowstone Center for Resources, National Park Service, Yellowstone National Park, Wyoming 82190, USA
5. Present address: Wildlife Veterinary Resources, P.O. Box 969, Gardiner, Montana 59030, USA
6. Wyoming State Veterinary Laboratory, Department of Veterinary Sciences, University of Wyoming, Laramie, Wyoming 82070, USA
7. Biology Department, Montana State University, Bozeman, Montana 59717, USA