Age-dependent survival of Herring Gulls across 14 contrasting colonies

Abstract

**Abstract:** Demographic rates such as recruitment and survival probability can vary considerably among populations of the same species, possibly due to spatially auto-correlated environmental processes. Breeding populations and foraging ranges are spatially segregated in colonial seabirds, making them ideal to study spatial patterns in demographic rates and their effects on local population dynamics. We investigated differences in age-dependent survival rates of Herring Gulls (Larus argentatus) breeding along the Dutch North Sea coast and we explored variation in survival among colonies in the context of their spatial distribution in the Netherlands. Between 1986 and 1988, per year approximately 100 nearly fledged individuals in 12-14 colonies received a unique colour ring, and birds have been resighted up until 2019 when at least one bird is known to be alive. We assessed whether survival until recruitment or until ten years old (their expected lifespan) explained variation in population trajectories of each colony. Juvenile and adult survival showed a strong, but different, north-to-south gradient in survival probability, while the spatial pattern of immature survival was less distinct. Recruitment nor the proportion of 10-year-old adults alive predicted whether a colony collapsed, declined, remained stable or increased. The distinct spatial pattern in survival suggests variation in regional food availability, which do not seem to drive local population dynamics. The absence of a link between survival and colony trajectories implies that connectivity between populations plays an important role affecting population dynamics. **Authors:** Rosemarie Kentie¹, Judy Shamoun-Baranes², Arie Spaans³, Kees Camphuysen⁴ ¹University of Amsterdam & Royal Netherlands Institute for Sea Research NIOZ, ²University of Amsterdam, ³retired from Wageningen Environmental Research ? WUR, ⁴Royal Netherlands Institute for Sea Research NIOZ