1. Behavioural Ecology Group, Section for Ecology & Evolution, Department of Biology, University of Copenhagen , Copenhagen 2100, Denmark
2. Institut Pluridisciplinaire Hubert Curien, Université de Strasbourg, CNRS, UMR 7178 , Strasbourg 67087, France
3. Department of Psychology and Department of Ecology and Evolutionary Biology, University of Tennessee , Knoxville, TN 37996, USA