1. Department of Ecosystem Science and Management Pennsylvania State University University Park PA 16802 USA
2. U.S. Geological Survey Patuxent Wildlife Research Center Laurel MD 20708 USA
3. U.S. Geological Survey Northern Rocky Mountain Science Center Aldo Leopold Wilderness Research Institute Missoula MT 59801 USA
4. Churchill Northern Studies Centre P.O. Box 610 Churchill MB R0B 0E0 Canada
5. Department of Biology Southeast Missouri State University One University Plaza MS 6200 Cape Girardeau MO 63701 USA