1. Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 14853, USA.
2. Department of Ecology, Evolution and Behavior, University of Minnesota, St. Paul, MN 55108, USA.
3. Department of Environmental Studies, Emory University, Atlanta, GA 30322, USA.
4. Cornell Laboratory of Ornithology, 159 Sapsucker Woods Road, Ithaca, NY 14850, USA.
5. Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA.
6. Institute of Ecosystem Studies, Box AB, 65 Sharon Turnpike, Millbrook, NY 12545, USA.
7. U.S. Geological Survey–National Wildlife Health Center, Madison, WI 53711, USA.