1. Department of Zoology; University of Oxford; Oxford OX13PS United Kingdom
2. Department of Collective Behaviour; Max Planck Institute for Ornithology; Universitätsstraße 10 78457 Konstanz Germany
3. Chair of Biodiversity and Collective Behaviour, Department of Biology; University of Konstanz; Universitätsstraße 10 78457 Konstanz Germany
4. Department of Plant Sciences; University of Oxford; Oxford OX13RB United Kingdom