1. Office National de la Chasse et de la Faune Sauvage; Unité Avifaune Migratrice, La Tour du Valat; Le Sambuc FR-13200 Arles France
2. Natural Sciences; Kristianstad University; SE-291 88 Kristianstad Sweden
3. Institut de Recherche de la Tour du Valat; Le Sambuc; FR-13200 Arles, France; and Office National de la Chasse et de la Faune Sauvage, Unité Avifaune Migratrice, La Tour du Valat; Le Sambuc FR-13200 Arles France
4. Section of Ecology; University of Turku; FI-20014 Turku, Finland; and Wetland Ecology Group, Department of Forest Sciences, P.O. Box 27 (Latokartanonkaari 7); FI-00014 University of Helsinki Finland
5. Department of Wildlife; Fish & Conservation Biology; University of California; Davis CA 95616-8627 USA