1. Conservation Biology Group, Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK.
2. Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720, USA.
3. Centre for Applied Conservation Research, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
4. Ghana Wildlife Division, Accra, Ghana.
5. Wildlife Conservation Society, Bronx, NY 10460, USA.