1. Department of Wildlife, Fish and Environmental Studies Swedish University of Agricultural Sciences (SLU) Skogmarksgränd 90183 Umeå
2. Department of Collective Behaviour, Max Planck Institute of Animal Behavior University of Konstanz Universitaetsstraße 10 78464 Konstanz Germany
3. Centre for the Advanced Study of Collective Behaviour University of Konstanz Universitaetsstraße 10 78464 Konstanz Germany
4. Department of Biology University of Konstanz Universitaetsstraße 10 78464 Konstanz Germany