1. Evolutionary Ecology of Variation Group; Max Planck Institute for Ornithology; Eberhard-Gwinner-Straße 82319 Seewiesen (Starnberg) Germany
2. Department Biology II, Behavioural Ecology; Ludwig-Maximilians-University of Munich; Großhadener Strasse 2 82152 Planegg-Martinsried Germany
3. Department of Biological Sciences; North Dakota State University; 1340 Bolley Drive Fargo ND 58102 USA