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MEPS prepress abstract   -  DOI:

Urban gulls with an anthropogenic diet still rely on marine resources

Joana Pais de Faria*, Patrícia T. Vaz, Catarina S. Lopes, Joana G. Calado, Jorge M. Pereira, Sara N. Veríssimo, Vitor H. Paiva, Ana M. M. Gonçalves, Jaime A. Ramos

*Corresponding author:

ABSTRACT: The availability of anthropogenic food subsidies has been promoting the increase of generalist opportunistic gull species, which currently breed and forage on predictable anthropogenic resources (e.g. landfills). Thus, we ask ourselves, are marine resources still important to urban dwelling gulls? We studied 4 natural and 2 urban yellow-legged gull Larus michahellis colonies and compared (1) diet composition (through pellet analysis) and (2) isotopic niches of adult birds and chicks, (3) diet delivered to chicks of different ages, and (4) fatty acid (FA) composition of fledglings, in order to assess diet composition, diversity and quality, and the relevance of marine prey for natural and urban gull populations. Adult urban gulls consumed considerably lower proportions of marine prey when compared to gulls from natural colonies; however, they fed their younger chicks (<20 d old) mostly with fish, representing 61 to 80% of their chick food deliveries. Refuse items were mostly delivered to chicks older than 20 d. Overall, urban isotopic niches were not completely distinct from those of natural colonies, sharing in some cases ca. 50% of their niche. Fledglings from the most urbanized colony presented overall higher FA concentrations and diversity, but they were lacking some omega-3 fatty acids relevant to animals’ physiology. Our results highlight the importance of marine resources for the diet of urban gulls, particularly during early chick rearing, the relevance of food sources in the area around the breeding colonies, and the fact that urban gulls benefit from year-round reliable anthropogenic food resources.