Spatial movements and habitat use of an opportunistic gull species in relation to their colony sites during the breeding season

The Yellow-legged Gull ( Larus michahellis ) is a widespread and opportunistic central-place forager during the breeding season, yet its spatial behavior and habitat use in Adriatic Sea remain poorly understood. Our aim was to investigate their foraging ranges, movement patterns, and habitat selection during the breeding season. In this study, we tracked 45 adult gulls from 9 breeding colonies distributed along the Adriatic coast using high-resolution GPS devices. Most individuals foraged relatively close to their breeding sites, typically within 20–50 km. However, some gulls demonstrated the capacity to travel much farther, especially when targeting predictable food sources such as landfills. Movement behavior varied notably among colonies, with individuals from more isolated, offshore colonies undertaking longer and more prolonged trips. Colony distance from the mainland emerged as a key factor influencing nest attendance, whereas colony size and sex had no significant effect. Across colonies, gulls predominantly exploited inland terrestrial habitats, particularly artificial areas, agricultural lands, and water bodies, while avoiding semi-natural and forested habitat. Given their ability to travel longer distances, they are able to exploit a wider range of foraging areas. While generally considered generalists, some individuals tended to forage in specific habitats, showing a certain degree of habitat specialization. Additionally, tracking data across multiple years revealed that while some birds reused the same foraging areas, others shifted locations, highlighting behavioral flexibility and individual-level plasticity. In the overall spatial area, no differences in habitat use were observed between sexes. However, within the core activity area, males showed stronger selection for artificial habitats, whereas females selected marine habitats, indicating potential foraging segregation between sexes. Spatial analysis showed that neighboring colonies were largely segregated in their foraging ranges, with limited overlap. Our findings demonstrate that Mediterranean Yellow-legged Gulls exhibit spatial and behavioral flexibility, with colony location strongly influencing foraging strategies and movement patterns. Their pronounced use of artificial habitats emphasizes the growing role of human-modified landscapes and anthropogenic food sources in shaping the ecology of this species.