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 use. 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. 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). Seasonal utilization distributions were estimated using weighted autocorrelated kernel density estimation (wAKDE). Home range and core area sizes differed among annual stages, with wintering ranges larger than breeding ranges. Ten individuals tracked across consecutive breeding seasons all returned to the same breeding colonies, and inter-annual home-range overlap and habitat-use similarity remained high across stages. Together, strong fidelity and seasonal habitat switching indicate reliance on repeatedly used key areas, while also suggesting potential vulnerability to ecological traps under rapid environmental change in the Yellow Sea.