1. Large Animal Research Group; Department of Zoology; University of Cambridge; Downing Street CB2 3EJ Cambridge UK
2. Behavioural Ecology Research Group; Department of Zoology; University of Cambridge; Downing Street Cambridge CB2 3EJ UK
3. School of Integrative Biology; University of Illinois; Urbana IL 61801 USA
4. Mammal Research Institute; University of Pretoria; Pretoria South Africa