1. Dept of Animal Ecology, Netherlands Inst. of Ecology Wageningen the Netherlands
2. Dept of Animal Ecology and Physiology, Radboud Univ. Nijmegen the Netherlands
3. Centre for Biodiversity Dynamics, Dept of Biology, Norwegian Univ. of Science and Technology Trondheim Norway
4. Wildfowl & Wetlands Trust Slimbridge Gloucestershire UK
5. Postkast 104 Haapsalu Estonia
6. Dept of Theoretical and Computational Ecology, Inst. for Biodiversity and Ecosystem Dynamics, Univ. of Amsterdam Amsterdam the Netherlands