Human activities do not affect all species in the same way and landscapes transformed by human development may still provide profitable environments for opportunistic species. These species are able to colonise these habitats, increasing their population sizes. This is the case of different avian species that are able to exploit the opportunities provided by humans in urban areas. In this project, we are investigating the spatial ecology, habitat use and trophic habits of the urban population of yellow-legged gull (Larus michahellis) of the city of Barcelona, and how these foraging-related aspects affect its pathogen load and dispersion, contaminant values and physiological state. We are combining individual marking programs (colour rings), GPS-tracking, trophic metrics (stomach content and isotopic markers), ecophysiological parameters, epidemiological measures (bacteria and virus) and pollution markers (PCBs and PCDEs). Preliminary results revealed that yellow-legged gulls mainly exploit urban habitats and human-related installations close to the city. Also, we found age-related differences in the spatial distribution. Regarding to the trophic habits, surprisingly, Barcelona’s yellow-legged gulls mainly exploit avian resources (urban pigeons and exotic parrots) followed by marine resources and food present in the garbage. Also, we found a dependence of part of the population to artificial feeding provided by humans. Spatial and trophic results explain the inter-individual differences in the pathogen and pollution results. In conclusion, this project is a clearly example of the importance of conduct multidisciplinary studies with wildlife living in urban ecosystems to understand how this species are adapted to human-related environments

12th European Ornithological Unión Congress (12th EOU), 26-30 August 2019, Cluj-Napoca, Romania