1. Laboratory of Reproductive Neuroendocrinology (G.E.B., S.T., H.C., N.P.), Max Planck Institute for Ornithology, 78315 Radolfzell, Germany
2. Department of Integrative Biology, and Helen Wills Neuroscience Institute (G.E.B.), Max Planck Institute for Ornithology, 78315 Radolfzell, Germany
3. University of California at Berkeley, Berkeley, California 94720-3140; and Department of Migration and Immuno-Ecology (M.H.), Max Planck Institute for Ornithology, 78315 Radolfzell, Germany