1. Division of Ecology and Evolution, Research School of Biology, Australian National University, Canberra 0200, Australian Capital Territory, Australia
2. Sovon Dutch Centre for Field Ornithology, PO Box 6521, 6503 GA Nijmegen, The Netherlands
3. Conservation Ecology Group, University of Groningen, 9700 CC Groningen, The Netherlands
4. Clinical Trials Unit, Department of Clinical Research, Institute of Social and Preventive Medicine (ISPM), University of Bern, Bern, Switzerland
5. Department of Animal Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands