Ardea
Official journal of the Netherlands Ornithologists' Union

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Swennen C. (1989) Gull predation upon Eider Somateria mollissima ducklings destruction or elimination of the unfit? ARDEA 77 (1): 21-46
Eider Somateria mollissima colonies in The Netherlands are situated in or near large gull colonies, mainly of Herring Gulls. The hatching success of the Eiders is high and shows a low variability, but fledging success is highly variable. Up to 99% of the ducklings may disappear during the first 10 days after hatching. Observations showed that the disappearance of the ducklings was mainly caused by predation of Herring Gulls. In this study it is shown by observations and experiments that gull predation is most heavy when the small ducklings are already severely weakened by scarcity of food. The survival of ducklings appears to be related to differences in their behaviour such as their reactions on the alarm signs by the female Eiders. Ducklings that, soon after hatching, were able to find and remain on some more constantly favourable sites for feeding, reacted adequately and had a high chance to survive.


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