Intrinsic and Extrinsic factors affecting the foraging behaviour of breeding Mediterranean gulls

During foraging, wild animals negotiate information with the surrounding environment, adopting specific behaviours to maintain an overall positive energy budget. To do so, generalist species exhibit a plastic foraging behaviour including flexible diet and habitat use, affected by both intrinsic (e.g. internal) and extrinsic (e.g. environmental) drivers. The Mediterranean Gull Ichthyaetus melanocephalus is a generalist feeder that can forage both at sea and on land during breeding. We investigated the drivers of choosing marine vs. land foraging by GPS tracking 20 breeding individuals across more than 1300 foraging trips. The average proportion of GPS fixes at sea per trip was 13%. Overall, birds foraged at sea more during chick-rearing compared to incubation stage, and males were more prone to face at sea trips than females. Both weather conditions and timing were found to be key drivers for foraging habitat choice, with at-sea foraging being more likely during late morning, under conditions of low precipitation, minimal wave activity, and at intermediate wind speeds. Our results highlight that the habitat foraging choice of this species depends on the interplay between both extrinsic and intrinsic factors and provide a novel insight into the fine-scale foraging movements of a generalist feeder.