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Cooperative breeding in the skuas (Stercorariidae): History, distribution and incidence

1994; Taylor & Francis; Volume: 24; Issue: 3 Linguagem: Inglês

10.1080/03014223.1994.9517469

1175-8899

Alan D. Hemmings,

Animal Behavior and Reproduction

Cooperative breeding, now well documented in birds, is generally confined to sedentary terrestrial families. It has not been reported amongst seabirds, with the exception of skuas (Stercorariidae). That apparently anomalous occurrence has implications for the conventional adaptive theories used to explain cooperative breeding. This paper examines the evidence for cooperative breeding across all nine skua species, and corrects some previous errors in that literature. It is shown that, away from the New Zealand temperate area, the incidence of trios is low, ranging from <1–5% of territories. These trios comprise polygynous and polyandrous associations. On temperate islands around New Zealand, a substantially higher incidence of trios (and larger groups) is found, sometimes reaching 30–50% of territories. The paper considers the area of higher trio incidence in more detail, drawing on the detailed examination which has been underway on the Chatham Islands over the past decade. Here, Catharacta lonnbergi breeds communally. Skua trios and groups in the Chathams are invariably polyandrous associations of one female and two or more males, in long lasting associations ‐ with some trios known to have been together for at least 14 years. In marked contrast to skua populations elsewhere, skuas in the New Zealand temperate region are non‐migratory.