Dispersal and Migratory Movements of Eiders Somateria mollissima Breeding in The Netherlands

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Abstract
Recoveries of dead (n = 3,158) and recaptures of live (n - 4,283) Eiders ringed in the Dutch Wadden Sea were analyzed. About 98% of the females ringed as ducklings showed natal philopatry; a few settled in adjacent colonies. Adult females were 100% philopatric. Inmales, natal dispersal was roughly estimated at 78%. Breeding dispersal in males was estiamted at 15% per year. Dispersing males settled in a large area up to about 1,700 km from their original colony. Post-fledging dispersal was in all directions, up to 1,200 km from the place of birth. The distribution of young males and females was similar up to the spring of their third calendar year. From then on, females were found near their natal colony and males were dispersed. This dispersal pattern can be explained by pair formation in the communal winter quarters and by the strong philopatry of the females. Males simply follow their mates ("abmigration"). The ultimate result of this dispersal behaviour is a genetic mixing of more than 40% per generation over a large area.