1. Cornell Laboratory of Ornithology and Department of Ecology and Evolutionary Biology, Cornell University, 159 Sapsucker Woods Road, Ithaca, NY 14850, USA
2. Smithsonian Tropical Research Institute, PO Box 2072, Balboa, Panama
3. Department of Biology, University of Missouri-St Louis, 8001 Natural Bridge Road, St Louis, MO 63121, USA