1. Metapopulation Research Group; Department of Biosciences; P.O. Box 65, 00014 University of Helsinki Helsinki Finland
2. Laboratoire d'Ecologie Alpine; UMR-CNRS 5553; Université Joseph Fourier; Grenoble I, BP 53 38041 Grenoble Cedex 9 France
3. Muséum National d'Histoire Naturelle; UMR 7204 MNHN-CNRS-UPMC; Centre de Recherches sur la Biologie des Populations d'Oiseaux; CP 51, 55 Rue Buffon 75005 Paris France
4. Department of Ecology and Evolutionary Biology; Yale University; 165 Prospect Street New Haven CT 06520-8106 USA
5. Department of Biology and Biotechnologies “Charles Darwin”; University of Rome “La Sapienza”; Viale dell'Università 32 Rome 00185 Italy