1. Colorado Cooperative Fish and Wildlife Research Unit; Department of Fish, Wildlife and Conservation Biology; Colorado State University; Fort Collins CO 80523-1403 USA
2. U.S. Geological Survey; Colorado Cooperative Fish and Wildlife Research Unit; Department of Fish, Wildlife and Conservation Biology; Colorado State University; Fort Collins CO 80523-1403 USA
3. Division of Migratory Bird Management; U.S. Fish and Wildlife Service; Lakewood CO 80215-5573 USA
4. University of Idaho; Moscow ID 83844 USA