1. US Geological Survey, Cooperative Fish and Wildlife Research Unit, Colorado State University, 201 J.V.K. Wagar Building, 1484 Campus Delivery, Fort Collins, CO 80523, USA.
2. Colorado Division of Wildlife, 317 West Prospect, Fort Collins, CO 80526, USA.
3. Department of Integrative Biology, University of Colorado, CB171, Denver, CO 80217, USA.