Sabine's Gull (Xema sabini) Nesting Aggregations in Western Alaska

Abstract

Abstract We analyzed data on the size of nesting aggregations of Sabine's Gulls (Xema sabini) observed in the Yukon–Kuskokwim Delta (YKD), Alaska, between 1986 and 2013, to determine whether the species is a “solitary low-density nester” there, as in other parts of its range. Data for 1087 nests show that 56% of Sabine's Gull nests were solitary and that <3% of aggregations exceeded 10 nests, although factors positively correlated with the evolution of colonial nesting, including exposure of nests to predators, aquatic habitat, and absence of feeding territories, apply to Sabine's Gulls nesting in the YKD. Although Sabine's Gulls in the YKD were most often solitary nesters, in 2010 we found a 102-nest aggregation on a small island in the study area, larger than any reported for the species. Among all aggregated nests, 75.4% occurred on islands, and only 13.9% along shorelines, while 39.8% of all solitary nests occurred on islands, and 39.3% along shorelines. The proportion of Sabine's Gull nests in the YK...