1. Behavioural & Physiological Ecology, University of Groningen , P.O. Box 11103 9700 CC, Groningen , The Netherlands
2. Department of Ecology and Evolution, University of Lausanne , Biophore - CH-1015, Lausanne , Switzerland
3. Department of Evolutionary Biology and Environmental Studies, University of Zurich , Winterthurerstrasse 190, CH- 8057, Zurich , Switzerland
4. School of Life Sciences, University of KwaZulu-Natal , Private Bag X01, Scottsville, 3209 , South Africa