1. School of Psychology, University of St Andrews, St Andrews, UK
2. Department of Primatology, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany
3. Budongo Conservation Field Station (BCFS), Masindi, Uganda
4. Department of Anthropology, Boston University, Boston, MA, USA
5. Wisconsin National Primate Research Center, Madison, WI, USA
6. Cognitive Science Centre, University of Neuchâtel, Neuchâtel, Switzerland