1. Colorado Cooperative Fish and Wildlife Research Unit; Department of Fish, Wildlife, and Conservation Biology; Colorado State University; Fort Collins Colorado 80523-1484 USA
2. Department of Natural Resources Science; University of Rhode Island; Kingston Rhode Island 02881-2018 USA
3. U.S. Geological Survey; Colorado Cooperative Fish and Wildlife Research Unit; Department of Fish, Wildlife, and Conservation Biology; Colorado State University; Fort Collins Colorado 80523-1484 USA