Unravelling urban nesting site selection in an opportunistic gull: an integrated analysis of micro-spatial habitat and litter quantification

The proliferation of gull populations in urban areas has led to an increase in human-gull conflicts, especially in highly populated cities where these opportunistic predators are often considered a nuisance. There is a lack of data regarding the selection of nesting sites by gulls, so management measures at nesting level cannot be implemented. Here, we investigated the main environmental factors that explain the nesting preferences of the yellow-legged gull (Larus michahellis) in urban areas, using the population in the city of Barcelona (NE Spain) as study model. We conducted an integrated analysis that combines micro-scale habitat selection assessments of 148 urban nesting sites with a macro-scale assessment of gull movements derived from GPS tracking of breeding yellow-legged gulls. We also analysed the type and abundance of litter in nests and main factors related to this. Nests were mainly found on flat roofs or above a structure on the main roof located at corner placements and situated on gravel substrate. Nest selection showed a negative relation to port distance and a building height beyond 12 m. The presence of litter was detected in more than 80% nests and was related to population density. Understanding the ecology of yellow-legged gulls in urban areas has implications for urban population management to prevent nest establishment.