1. Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK.
2. Mammal Research Institute, University of Pretoria, 0002 Pretoria, South Africa.
3. Institute of Cell, Animal and Population Biology, University of Edinburgh, King's Buildings, West Mains Road, Edinburgh EH9 3JT, UK.
4. Conservation and Research Center, Smithsonian Institution, 1500 Remount Road, Front Royal, VA 22630, USA.