Distribution and habitat use by the Audouin's Gull (Ichthyaetus audouinii) in anthropized environments

Abstract

Human activities provide wildlife with highly abundant and predictable food subsidies, which can affect population dynamics and have wide-ranging ecological impacts. A key ecological question is how species adapt their foraging behaviour to capitalize on these new feeding opportunities. We investigate habitat use by Audouin's Gulls (Ichthyaetus audouinii) off the Western Mediterranean Sea, an opportunistic seabird that has recently expanded to diverse breeding colonies subjected to varying degrees of human influence. By combining GPS tracking, remote sensing, and GIS, we assessed the resource selection and habitat preferences of gulls from five colonies across their breeding latitudinal range, including interactions with industrial fisheries. Overall, the use of terrestrial habitats was slightly higher (57 % of total positions) compared to the marine environment (42 %), with individuals preferentially feeding on urban and related areas or fishing ports. However, habitat utilization varied among studied colonies, likely in response to contrasting food availability and accessibility of human related food resources on land (e.g., agriculture and livestock areas, landfills or rice fields). At sea, individuals largely distributed over highly productive and persistent marine areas with intense fishing pressure. Individuals also adapted their daily activity patterns to match food availability: gulls preferentially feed on the marine environment during the night, while the use of terrestrial habitats increases during daylight hours. Individuals' daily activity patterns also matched that for the two main fishing gears operating in the area: diurnal trawlers and nocturnal purse-seiners. Our findings offer perspectives on the reliance of opportunistic seabird species on anthropogenic food subsidies and inform on potential implications for the conservation and management of these under changes in fishing policies (EU discard ban). Broadly, we provide further insights on how this species can adapt to changing environments.