1. Department of Biology, University of Konstanz, 78464 Konstanz, Germany
2. Department for the Ecology of Animal Societies, Max Planck Institute of Animal Behavior, 78467 Konstanz, Germany
3. Kalahari Research Centre, 8467 Van Zylsrus, Northern Cape, South Africa
4. Department of Evolutionary Biology and Environmental Studies, University of Zurich, 8057 Zurich, Switzerland
5. Interdisciplinary Center for the Evolution of Language, University of Zurich, 8057 Zurich, Switzerland
6. Biological Sciences, Brock University, St. Catharines, ON, Canada, L2S 3A1