1. Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, USA.
2. Department of Anthropology, University of California, Davis, Davis, CA, USA.
3. Smithsonian Tropical Research Institute, Panama.
4. Edward Grey Institute of Field Ornithology, Department of Zoology, University of Oxford, Oxford, UK.
5. Department of Collective Behaviour, Max Planck Institute for Ornithology, Konstanz, Germany.
6. Chair of Biodiversity and Collective Behaviour, Department of Biology, University of Konstanz, Konstanz, Germany.