The reproductive behaviour and ecology of Sabine's gulls (Xema sabini) in the eastern Canadian Arctic

Life history theory focuses on how phenotypic traits interact to determine an organism's fitness, which is generally measured in terms of survival and reproduction. An animal's behaviour is a critical component in its ability to survive and reproduce, because natural selection promotes individuals that are behaviourally efficient. -- Like many avian species breeding at high latitudes, the reproductive behavior and ecology of Sabine's Gull (Xema sabini) has been rarely studied. This species nests in coastal wetland tundra across the Arctic, and winters at cold-water upwelling zones in the Tropics and Subtropics. It is considered an atypical gull, both morphologically and behaviourally, and is recognized as phylogenetically distinct. -- At East Bay, Southampton Island, Nunavut, Sabine's Gulls nested on mossy edges of freshwater ponds, and were non-randomly distributed across the study area and within nesting habitat. Compared with other gulls, they exhibit several distinct ecological traits. They had relatively short incubation and fledging periods, and, within 24 hours of hatching, families relocated to post-hatching territories at the shoreline. These aspects of their reproductive ecology, which differ from other gulls, are likely adaptive traits that have evolved in response to specific characteristics of their Arctic breeding areas. -- Sabine's Gulls also exhibit a number of behavioural traits that are typical of gulls. Pairs showed strong site-tenacity and mate-fidelity from year to year. Throughout incubation and early brooding, males and females showed high reproductive investment. Overall, they shared parental duties equally, although there was considerable variation among pairs. Sabine's Gulls distinguished between threatening and non-threatening species close to their nests, and both members of a pair were aggressive towards predators. Although the relative intensity of response did not change over time, it did differ among predator types. Reproductive success was variable among years, and indirectly influenced by availability of microtine rodents, via their shared predators. The local annual survival rate, estimated at 0.89 ± 0.04, was close to those of other gull and tern species. -- Overall, the evolution of Sabine's Gull life history traits appears to have been influenced by both their phylogeny and the particular ecological conditions of their breeding environment, and/or interactions between these