Some seabirds commonly use artificially reclaimed lands, which are frequently located next to mainland environments, for breeding. Nest predation risk caused by birds or mammals from the mainland has negative influence on fitness-related costs and distribution of seabirds. Here, we sought to link potential factors, specifically those related to nest predation and nest environment, with breeding performance and colony movements of the Saunders's gull (Saundersilarus saundersi), a vulnerable species, on a large reclaimed area (1350 ha) in Incheon in Republic of Korea. This reclaimed area has experienced rapid changes in communities of nest predators from the mainland and vegetation ranging from halophytes to terrestrial plants after reclamation. Additionally, changes in the surrounding of used nest sites were retrospectively examined to determine whether colony movement was reversible in this reclaimed area. Our results indicated that high nest predation in a previous year induced colony movements in a consecutive year while the breeding colony exhibited a gradual reduction in clutch size. However, such movement after high nest predation seemed to be irreversible due to ongoing habitat degradation caused by construction and vegetation alteration. This study highlights that high nest predation may exert strong pressure on breeding colonies of Saunders's gulls. It also has anthropogenic impacts, leading to continuous dispersal of colonies to new areas for this vulnerable seabird in a reclaimed land.
Keywords: Saunders's gull; clutch size; colony movement; nest predation; reclamation.