Plumage polymorphism and kleptoparasitism in the Arctic Skua Stercorarius parasiticus
Atlantic seabirds , Volume 4 - Issue 2 p. 41- 52
The Arctic Skua Stercorarius parasiticus is polymorphic, expressing a roughly clinal variation in plumage from the northern to the southern end of its breeding range. It has been suggested – but never confirmed – that the maintenance of this polymorphism may be related to their role as specialist kleptoparasites of other birds, through either predator apostatic selection, or selection for cryptic advantage. The southern breeding population of Handa Island, Scotland, was studied during the summer of 2000. Various aspects of 1421 attacks on Common Guillemots Uria aalge were recorded, and tested for differences in behaviour and outcome between the morphs. No differences were found in relation to chase success rates, methods of attack, or the response of their victims. It is concluded that the polymorphism of this species is unrelated to its kleptoparasitic behaviour. Some other possible explanations for the plumage variation are briefly discussed.
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