1. Netherlands Institute of Ecology (NIOO-KNAW), PO Box 1299, 3600 BG Maarssen, The Netherlands
2. Swiss Ornithological Institute, Luzernstrasse, 6204 Sempach, Switzerland
3. Behavioural Ecology Research Group, University of Debrecen, 4010 Debrecen, Hungary
4. SOVON Dutch Centre for Field Ornithology, PO Box 59, 1790 AB Den Burg (Texel), The Netherlands
5. School of Environment and Society, University of Swansea, Swansea SA2 8PP, UK
6. Department of Mathematics, University of Bristol, University Walk, Bristol BS8 1TW, UK