Seasonal utilization distributions, site fidelity, and habitat use of the Black-tailed Gull (Larus crassirostris) in the Yellow Sea

Movement shapes biodiversity patterns and ecosystem functioning, and recent advances in animal tracking have improved our ability to quantify space usage. Utilization distributions, site fidelity, and habitat use provide complementary perspectives on where animals concentrate their activity and how consistently they reuse key areas, informing conservation and habitat management. Black-tailed Gulls ( Larus crassirostris ) are abundant in the Yellow Sea, yet their fine-scale seasonal space use and fidelity patterns remain poorly quantified. Here, we estimated their seasonal home ranges and core areas and evaluated site fidelity, comparing them among seasons. From 2020 to 2024, we tracked 15 adult Black-tailed Gulls with GPS loggers on the west coast of the Korean Peninsula for 496–850 days per individual. Breeding, non-breeding, and wintering sites were delineated using hierarchical density-based spatial clustering of applications with noise (HDBSCAN), and seasonal utilization distributions were estimated using weighted autocorrelated kernel density estimation (wAKDE). Site fidelity was quantified as the breeding-site return rate, inter-annual home-range overlap, and habitat-use similarity, and habitat use was compared among annual stages. Home ranges and core area sizes differed among annual stages, with wintering ranges larger than breeding ranges. Ten individuals could be tracked across consecutive breeding seasons, all of which returned to the same breeding colonies, yielding a 100% breeding-site return rate. Inter-annual home-range overlap and habitat-use similarity were high and did not differ among annual stages. In contrast, habitat use differed among stages. Together, strong fidelity and seasonal habitat switching suggest reliance on repeatedly used key areas that may become maladaptive under the rapid environmental change present in the Yellow Sea, increasing the risk of fidelity-induced ecological traps. Conservation planning should prioritize repeatedly used key habitats and incorporate season-specific spatial and habitat requirements, including the protection of breeding colonies and the intertidal and marine habitats used during non-breeding and wintering periods.