1. Max Planck Institute of Animal Behavior, Department of Collective Behavior, Universitätsstraße 10, Konstanz 78457, Germany.
2. University of Konstanz, Department of Biology, Universitätsstraße 10, Konstanz 78457, Germany.
3. University of Konstanz, Center for the Advanced Study of Collective Behaviour, Universitätsstraße 10, Konstanz 78457, Germany.
4. Kenya Wildlife Service, P.O. Box 40241-001000, Nairobi, Kenya.
5. Department of Ornithology, National Museums of Kenya, P.O. Box 40658-001000, Nairobi, Kenya.