Distribution of breeding sites and food constrains size and density of yellow-legged gull colonies

In this study, we aimed to identify the factors determining the size and density of yellow-legged gull colonies (Larus michahellis) on rocky islands. We considered both island geography and topography, as well as food resources availability, as potential constraining factors. Our censuses conducted on 43 islands and islets along 80 km of the French Mediterranean coastline contained the largest French yellow-legged gull populations (20 914 breeding pairs). Multiple linear regression models determined that colonization history and island area primarily determine colony size (R-2 = 88.3%). Gull population density was also associated to colonization history, island characteristics, anthropogenic food resource availability, and human activities (R-2 = 63.7%). We conclude that breeding site selection by yellow-legged gulls seems to fulfill the known topographic requirements for the breeding sites of this species while minimizing the distance to its known foraging habitat in the area (landfills).