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We studied the reproductive biology of Sabine’s Gulls (Xema sabini) breeding on Southampton Island, in the eastern Canadian Arctic, from May to August in 1998 and 1999, and compared our results to information collected from the same region in 1980. Breeding phenology was 10 days earlier in 1998 than in these other years, and reflects an earlier onset of snowmelt in that year. Nests were dispersed, with a density of 7.6 to 8.7 nests per km(2). Sabine’s Gulls exhibited strong interannual fidelity to breeding sites. Mean clutch size was lower in 1999 than 1998, and lower in both these years than in 1980. Hatching success was 63% in 1998, but only 21% in 1999 due to increased predation, most likely by arctic fox (Alopex lagopus). Adult gulls and chicks abandoned nest-sites within a few hours of the hatching of the last chick and relocated to coastal ponds, where adults continued to attend chicks. In comparisons of the reproductive biology of Sabine’s Gull to closely related "tern-like" gull species arid other "black-headed" gulls, Sabine’s Gull showed a number of distinct ecological and behavioral differences and represents an ecological outlier within the Laridae.