Systematic observations of staging dabbling ducks through 24 autumns (1978 to 2001) in a Danish wetland show that the numbers of the numerous species Eurasian Wigeon (Anas penelope), Eurasian Teal (Anas crecca) and Mallard (Anas platyrhynchos) were positively and only correlated and with the water level. For the less numerous species, Northern Shoveler (Anas clypeata) and Northern Pintail (Anas acuta), the correlation with the water level was less evident, and an effect of the overall size of the flyway population was demonstrated. The increasing numbers recorded with rising water level may have two explanations or probably a combination. One is redistribution of birds migrating through the region, reflecting that the available habitat limits the numbers of ducks recorded, and the other is prolonged stay for individual birds when conditions are favorable. The relationship between average seasonal water level and average number of ducks were modelled to estimate a minimum favorable water level to be maintained throughout the autumn, a tool proposed for optimizing the site for staging dabbling ducks.
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Vol. 29 • No. 1