1. Terrestrial Ecology Unit, Department Biology Ghent University, K. L. Ledeganckstraat 35, B-9000 Gent, Belgium
2. Bionet Natuuronderzoek, Valderstraat 39, 6171EL, Stein, The Netherlands
3. Animal Ecology & Ecophysiology group, Institute for Water and Wetland research, Radboud University Nijmegen, P.O. Box 9010, 6500GL Nijmegen, The Netherlands
4. Ad Hoc Zoogdieronderzoek, Oude Velperweg 34, 6824HE, Arnhem, The Netherlands
5. Department of Behavioural Ecology and Evolutionary Genetics, Max Planck Institute for Ornithology, Eberhard-Gwinner-Strasse, 82319 Seewiesen, Germany