Nesting the city: long-term spatiotemporal dynamics of nest distribution in a synanthropic gull within a high density European city

Abstract Urbanization alters biodiversity by displacing some species while favouring others that exploit human-modified environments. The Yellow-legged gull ( Larus michahellis ) is a successful urban colonizer in southern Europe, yet little is known about the spatiotemporal factors influencing its nesting distribution in cities. Using a 12-year dataset (2013–2024) from citizen reports and management interventions in Barcelona (Spain), we examined the nest density and potential breeding population size, temporal changes in spatial distribution, and the main environmental predictors of nest density. Spatial density analyses revealed consistent hotspots near the city center and coast, with occasional shifts toward northeastern districts. On average (and standard deviation), nest detections by year were 262 ± 61, corresponding to an estimated range 314–509 breeding pairs after accounting for nests not detected. Spatial Generalized Additive Models (GAMs) identified building height as a significant predictor for all years. Proximity to port, green areas and the coast, had significant effects with year variation. Our findings suggest that structural characteristics of the urban landscape and proximity to foraging habitats, drive nest-site selection. This work provides the first robust estimate of Barcelona’s urban gull breeding population and highlights priority areas for targeted management. By integrating citizen reports with spatial modelling, authorities can optimize monitoring, resource allocation, and conflict mitigation strategies, promoting coexistence between urban wildlife and residents.