The Breeding Behaviour of Sabine's Gull, Xema Sabini

Abstract

[Sabine's Gull, Xema sabini is a morphologically aberrant gull, breeding in the Arctic. This paper describes its breeding behaviour, as recorded in the region of Hooper Bay, W. Alaska (61° 35' N, 166° 05' W) in the summer of 1960. The object of this study has been, not just to describe the behaviour, but to try to relate it to the species' ecology, and also, by comparisons with other gulls, to clarify the taxonomic position of Sabine's Gull. Much of Sabine's Gull behaviour is similar to that of other gulls, but there are some aberrancies which occur either rarely or not at all in other species. Chief among these are the Quarter Upright, the emphasis on Hunched, as opposed to Upright, postures, the attraction of unmated females by Arch-and-Bow rather than Long Call, the direct feeding (as opposed to regurgitation) of the female early in the season, the rarity of Head Tossing in courtship feeding and copulation, and the throwback and Crouch in the Long Call postures. Evidently, Sabine's Gull is behaviourally as well as morphologically aberrant. It seems to be most closely related to such species as Franklin's Gull, Larus pipixcan. Contrary to MOYNIHAN'S (1959) suggestion, based on morphological criteria, there is no evidence of any relationship with the Swallowtailed Gull, Creagrus furcatus. The functions of the grey and black hood are discussed. It is also suggested that some of Sabine's Gull's morphological and behavioural peculiarities may be related to its breeding in small, loose groups rather than in dense colonies, on the flat tundra, and during the short Arctic summer. A partial analysis of the motivation of the agonistic and sexual behaviour was also made. The relations of the various agonistic postures to the tendencies to flee and attack are discussed. It is also concluded that the different postures adopted during the loud-calling phase of the Long Call depend on the position of the opponent and not on any motivational differences. The sexual behaviour seems to consist of two relatively independent systems - the Meeting Ceremony and Luring. The interrelationships of the different patterns in Luring are analysed in more detail., Sabine's Gull, Xema sabini is a morphologically aberrant gull, breeding in the Arctic. This paper describes its breeding behaviour, as recorded in the region of Hooper Bay, W. Alaska (61° 35' N, 166° 05' W) in the summer of 1960. The object of this study has been, not just to describe the behaviour, but to try to relate it to the species' ecology, and also, by comparisons with other gulls, to clarify the taxonomic position of Sabine's Gull. Much of Sabine's Gull behaviour is similar to that of other gulls, but there are some aberrancies which occur either rarely or not at all in other species. Chief among these are the Quarter Upright, the emphasis on Hunched, as opposed to Upright, postures, the attraction of unmated females by Arch-and-Bow rather than Long Call, the direct feeding (as opposed to regurgitation) of the female early in the season, the rarity of Head Tossing in courtship feeding and copulation, and the throwback and Crouch in the Long Call postures. Evidently, Sabine's Gull is behaviourally as well as morphologically aberrant. It seems to be most closely related to such species as Franklin's Gull, Larus pipixcan. Contrary to MOYNIHAN'S (1959) suggestion, based on morphological criteria, there is no evidence of any relationship with the Swallowtailed Gull, Creagrus furcatus. The functions of the grey and black hood are discussed. It is also suggested that some of Sabine's Gull's morphological and behavioural peculiarities may be related to its breeding in small, loose groups rather than in dense colonies, on the flat tundra, and during the short Arctic summer. A partial analysis of the motivation of the agonistic and sexual behaviour was also made. The relations of the various agonistic postures to the tendencies to flee and attack are discussed. It is also concluded that the different postures adopted during the loud-calling phase of the Long Call depend on the position of the opponent and not on any motivational differences. The sexual behaviour seems to consist of two relatively independent systems - the Meeting Ceremony and Luring. The interrelationships of the different patterns in Luring are analysed in more detail.]