1. Department of Zoology and Museum of Vertebrate Zoology, University of California, Berkeley, California, U.S.A.
2. Field Museum of Natural History, and Department of Anatomy, University of Illinois at the Medical Center, Chicago, U.S.A.
3. Max‐Planck‐Institut für Verhaltensphysiologie, 8131 Seewiesen, Obb., Germany