Abstract
Anthropogenic habitat change is having a detrimental impact on biodiversity worldwide, altering the foraging behaviour and population dynamics of many species. Generalist species often adapt by broadening their resource use and/or exploiting human-modified environments. However, habitat changes that reduce the availability of good quality resources can lead to increased interspecific competition among sympatric species and increased conflict with human activities. We investigated the breeding season foraging ecology of three sympatric gull species, Lesser Black-backed (Larus fuscus), Herring (Larus argentatus) and Great Black-backed Gulls (Larus marinus), from the same colony in Scotland. Using GPS tracking data, we analysed foraging ranges, spatial distributions and habitat preferences to determine the extent of the gulls' niche partitioning and use of human-modified landscapes. Our findings revealed considerable overlap in resource use between species. However, species-level differences in spatial distributions and habitat selection demonstrated partial niche partitioning. Lesser Black-backed Gulls had significantly larger foraging ranges than Herring and Great Black-backed Gulls, indicating spatial segregation. Herring and Great Black-backed Gulls strongly selected for landfill and coastal habitats. Lesser Black-backed Gulls also selected for these habitats but primarily used agricultural areas. Individual-level analysis revealed that most species-level selection for urban, landfill and harbour habitats was driven by a subset of individuals. The observed limited niche partitioning indicates that further habitat loss or degradation could negatively impact all three gull species unless the extent of niche partitioning changes. Given that most habitats used were linked to human activities, further anthropogenic change may displace gulls from preferred foraging areas, increasing competition for limited resources and exacerbating conflicts with human activities in alternative habitats. By simultaneously tracking sympatric species, we can better understand how shifts in resource availability may impact interspecific competition and interactions with human activities to help inform management actions and mitigate conflict with humans, particularly around licensed control.