1. Research Group Evolutionary Ecology of Variation; Max Planck Institute for Ornithology; Eberhard-Gwinner-Strasse 7 82319 Seewiesen Germany
2. Conservation Ecology Group; Groningen Institute for Evolutionary Life Science (GELIFES); University of Groningen; PO Box 11103 9700 CC Groningen The Netherlands
3. Behavioural Ecology; Department of Biology; Ludwig Maximilians University of Munich (LMU); Großhadener Str. 2 82152 Planegg-Martinsried Germany