Local dietary adaptations of the yellow-legged gull Larus michahellis: responding to human-induced changes in food availability

As human activities continue to reshape ecosystems, understanding wildlife adaptations is crucial in ecology. This study examines how the opportunistic yellow-legged gull Larus michahellis adjusts its diet and foraging behaviour during breeding to new, human-related feeding opportunities in a highly humanized region of the southern Iberian Peninsula. Specifically, we combined Global Positioning System tracking technology, Geographic Information Systems and stable isotope analysis (SIA) to assess habitat choice and resource selection in relation to habitat characteristics and human activities, both on land and at sea, across 4 gull colonies. Overall, gulls exhibited a generalist foraging behaviour, with terrestrial habitats preferred over marine (61.87 vs. 38.13%, respectively). However, habitat utilisation patterns differed among colonies. SIA confirmed the incorporation of both terrestrial and marine resources in the diet, also with important differences among colonies. Additionally, a significant proportion of foraging activity was recorded in urban and highly exploited marine areas, underscoring the notable influence of human activity and the dependency of the species on anthropogenic food subsidies. This study reinforces previous knowledge about the trophic plasticity of this species. Through a holistic approach, the results indicate the extent to which local and sometimes differential adaptations in resource use may arise in response to specific human activities. In the context of highly regulatory policies for the management of landfills and fisheries, future studies should monitor the responses of these organisms to sudden shifts in the availability of predictable anthropogenic food subsidies.