Year-round colony-level differences in foraging behaviour and diel activity of yellow-legged gulls from natural and urban colonies

Abstract

Urbanisation has led to increased populations of opportunistic species like gulls, driven by the availability of anthropogenic resources. However, gulls may exhibit distinct foraging strategies, spatially and temporally, especially when foraging in urban versus natural habitats. We compared the spatial ecology of yellow-legged gulls Larus michahellis from Porto (urban) and Berlenga Island (natural), using GPS-GSM transmitters to track foraging behaviour across breeding and wintering seasons. Our data revealed that gulls from Berlenga travelled farther and took longer foraging trips, while urban gulls showed little seasonal dispersion, highlighting urban influences on foraging. Urban gulls favoured urban habitats, while natural colony gulls foraged primarily at sea and in fishing harbours, though individual differences were observed. Despite not differing greatly between workdays and weekends, daily rhythms revealed distinct patterns among habitats used and between colonies, implying that gulls adapted their foraging activity to match human routines. Our findings indicate that variation in the foraging ecology and distribution of yellow-legged gulls is related to the characteristics of each breeding site and that human activity and consequent environmental changes influence the behaviour of these natural and urban-dwelling birds in different ways.