1. Minnesota Cooperative Fish and Wildlife Research Unit Department of Fisheries, Wildlife, and Conservation Biology University of Minnesota St. Paul Minnesota 55108 USA
2. Department of Environmental Sciences University of Toledo Toledo Ohio 43606 USA
3. Department of Environmental Science, Policy, and Management University of California Berkeley California 94720 USA
4. U.S. Geological Survey Minnesota Cooperative Fish and Wildlife Research Unit University of Minnesota St. Paul Minnesota 55108 USA
5. Department of Forestry, Wildlife, and Fisheries University of Tennessee Knoxville Tennessee 37966 USA