1. Department of Primatology, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany.
2. Budongo Conservation Field Station, Masindi, Uganda.
3. School of Psychology and Neuroscience, University of St. Andrews, St. Mary’s Place, St. Andrews, Fife KY16 9JP, UK.
4. Cognitive Science Centre, University of Neuchâtel, Neuchâtel, Switzerland.