1. Biophysics Graduate Group, University of California at Berkeley, Berkeley, CA 94720-3200, USA
2. Department of Environmental, Science, Policy, and Management, University of California at Berkeley, Berkeley, CA 94720-3112, USA
3. Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa
4. BioCentrum Amsterdam, de Boelelaan 1087, NL-1081 HV Amsterdam, The Netherlands