1. Museum of Vertebrate Zoology, University of California, Berkeley, CA 94720, USA.
2. Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA 50010, USA.
3. Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA 94720, USA.
4. San Francisco Estuary Institute, Richmond, CA 94804, USA.
5. Department of Birds and Mammals, San Diego Natural History Museum, San Diego, CA 92101, USA.
6. Department of Biology, University of New Mexico, Albuquerque, NM 87131, USA.