1. Centre for Social Learning and Cognitive Evolution, and Scottish Primate Research Group, School of Psychology and Neuroscience, University of St Andrews, St Andrews KY16 9JP, UK.
2. Inkawu Vervet Project, Mawana Game Reserve, Swart Mfolozi, KwaZulu Natal 3115, South Africa.
3. Institute of Biology, University of Neuchâtel, 2000 Neuchâtel, Switzerland.