1Department of Organismic Biology, Ecology, and Evolution, and Centerfor Tropical Research, Institute of the Environment, 621 Charles E. Young Drive South, Room LS5120, University of California, P.O. Box 951606, Los Angeles, California 90095-1606, USA; 2Smithsonian Environmental Research Center, P.O. Box 28, 647 Contees Wharf Road, Edgewater, Maryland 21037-0028, USA; 3School of Biological Sciences, Washington State University, P.O. Box 644236, Pullman, Washington 99164-4236, USA; Cornell Laboratory of Ornithology, 159 Sapsucker Woods Road, Ithaca, New York 14850, USA; 5Department of Evolution, Ecology, and Organismal Biology (EEOB), Ohio State University, 1735 Neil Avenue, Columbus, Ohio 43210-1293, USA; 6Department of Biological Sciences, Hanover, Dartmouth College, New Hampshire 03755, USA; 7Canadian Wildlife Service, 115 Perimeter Road, Saskatoon, Saskatchewan S7N 0X4, Canada; and 8Burke Museum, University of Washington, Box 353010, Seattle, Washington 98195-3010, USA