1. Behavioural Ecology, Institute of Ecology and Evolution, University of Bern, Wohlenstrasse 50a, 3032 Hinterkappelen, Switzerland
2. Department of Sociobiology/Anthropology, Johann-Friedrich-Blumenbach Institute for Zoology and Anthropology, University of Göttingen, Kellnerweg 6, 37077 Göttingen, Germany
3. Behavioural Ecology and Sociobiology Unit, German Primate Center, Leibniz Institute for Primate Research, 37077 Göttingen, Germany
4. Department of Collective Behavior, Max Planck Institute of Animal Behavior, 78467 Konstanz, Germany
5. Institute for Advanced Study (Wissenschaftskolleg zu Berlin), 14193 Berlin, Germany