1. Cornell Lab of Ornithology, 159 Sapsucker Woods Road, Ithaca, New York 14850 USA
2. Department of Neurobiology and Behavior, Cornell University, Ithaca, New York 14853 USA
3. School of Biological Sciences, University of Nebraska, 348 Manter Hall, Lincoln, Nebraska 68588 USA
4. 145 Eldridge Avenue, Mill Valley, California 94941 USA