Affiliation: | SOVON Dutch Centre for Field Ornithology, Rijksstraatweg 178, 6573DG Beek-Ubbergen, The Netherlands; Alterra, Wageningen University and Research Centre, PO Box 47, 6700 AA Wageningen, The Netherlands, and Dutch Centre for Avian Migration and Demography, Netherlands Institute of Ecology (NIOO-KNAW), PO Box 40, 6666 ZG Heteren, The Netherlands |