1. Cornell University 1 Department of Ecology and Evolutionary Biology , , Ithaca, NY 14853 , USA
2. Cornell University 2 Cornell Lab of Ornithology , , Ithaca, NY 14850 , USA
3. University of Arizona 3 Department of Ecology & Evolutionary Biology , , Tucson, AZ 85719 , USA
4. Colby College 4 Department of Biology , , Waterville, ME 04901 , USA