THE DISTRACTION BEHAVIOUR OF THE ARCTIC SKUA

• Published in: Ibis
• Main Author: Williamson, Kenneth
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1949
• Subjects: Arctic; Arctic skua; Stercorarius parasiticus
• Online Access: http://dx.doi.org/10.1111/j.1474-919x.1949.tb02269.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1474-919X.1949.tb02269.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1474-919X.1949.tb02269.x

Summary. Distraction displays of the Arctic Skua Stercorarius parasiticus were studied in the Faeroe Islands in colonial nesters and a solitary pair. There are aggressive and passive forms. The aggressive flight against human intruders is common throughout the nesting cycle in the colony, but absent from the behaviour of solitary pairs. It is suggested that its development is correlated with an internal rhythm which requires a certain level of mutual stimulation not attainable by solitary or widely‐scattered pairs. A highly formalized version of the attacking flight was employed against a sheep, in which the pair showed a marked tendency to coordinate their movements. The lure display when eggs are fresh is markedly different from that employed nearer the hatching‐period and afterwards. A courtship posture appears as a substitute activity in the early period, but only in the presence of the mate. In the solitary pair development of the normal lure display was gradual, reaching its peak towards the hatching‐period: there is a marked tendency for the pair to perform together, deriving mutual stimulation. It is suggested that this factor is important in the colony, where several perform together in scattered groups, in ensuring the earlier development (and therefore increased survival value) of the lure display. The birds' movements emphasize contrasts in the plumage coloration, and therefore the pattern may have greater biological advantage for colonies of predominantly light‐phase birds in areas of fox predation. The various patterns are described, and also variations incorporating false‐brooding and drinking motions. The main components of the patterns are probably derived from the primitive food‐begging of the chick, and elaborated with actions from courtship display.