1. Department of Behavioural Ecology and Evolutionary Genetics; Max Planck Institute for Ornithology; Eberhard-Gwinner-Strasse 82319 Seewiesen Germany
2. Department of Biology; Terrestrial Ecology Unit; Ghent University; K.L.Ledeganckstraat 35 B-9000 Gent Belgium
3. Zoological Institute & Museum; Greifswald University; J.-S.-Bach-Str. 11/12 D-17489 Greifswald Germany