Nest predation and nest site selection among EidersSomateria mollissima:the influence of gulls

Abstract

Hooded Crows Corvus cornix, Great Black‐backed GullsLarus marinusand Herring Gulls L. argentatus were the main nest predators in an Eider population in southwest Sweden. The clutch sizes of Eider nests within gull colonies did not differ from those outside gull colonies. The proportion of Eider nests destroyed by predators was significantly lower within than outside gull colonies, especially on islands with Lesser Black‐backed Gulls L. fuscus. Although the difference was not significant, the survival time of simulated Eider nests was higher within than outside gull colonies. On Eider islands with gull colonies, foraying crows spent more time within the colony area than expected by chance. However, crows apparently avoided an area around each gull nest, and we suggest that the colonies, to some extent, protected Eider nests against predation. The density of Eider nests was higher on gull islands than on gull‐ free islands, and higher within than outside the gull colonies. However, the association with gulls was weak compared to that displayed by some other waterfowl.