Territory size, breeding time and mating preference in the Arctic skua

Abstract

THE Arctic skua is a polymorphic seabird with three phenotypes in plumage—pale, intermediate and dark. The dates during the breeding season when new pairs breed are related to the phenotypes of the males^1,2: on average, dark males breed before intermediate males who breed before pale males. This effect is most pronounced when the male has no previous breeding experience³. These observations can be explained by assuming that females have mating preferences for the darker males^2,4. Each breeding pair of Arctic skuas defends a territory: some defend their territories very strongly, attacking intruders viciously, others seldom attack. In the red grouse, androgen levels have been shown to determine both aggression and mating success of males⁵. We show here that the size of a male's territory may either correlate with breeding time and mating preference through a common cause, or determine them both directly.