1. Department of Migration and Immuno-ecology, Max Planck Institute for Ornithology, Am Obstberg 1, 78315 Radolfzell, Germany
2. Centre d'Ecologie Fonctionnelle et Evolutive, UMR 5175 CNRS-Université de Montpellier- EPHE-Université Paul Valery, 1919 Route de Mende, 34293 Montpellier cedex 5, France
3. Department of Biology, University of Konstanz, Universitätsstr. 10, 78464 Konstanz, Germany