1. Saint Louis Zoo, One Government Drive, Saint Louis, Missouri 63110, USA
2. College of Veterinary Medicine, University of Missouri, 203 Veterinary Medicine Building, Columbia, Missouri 65211, USA
3. Current address: Utah's Hogle Zoo, 2600 E. Sunnyside Avenue, Salt Lake City, Utah 84108, USA
4. Wildlife Conservation Research Unit, University of Oxford, Tubney House, Abingdon Road, OX13 5QL, UK
5. Department of Biology, University of Missouri—Saint Louis, 8001 Natural Bridge Road, Saint Louis, Missouri 63121, USA
6. Institute of Ecology, The University of Georgia, Athens, GA 30602, USA