First fatty acid analysis in a threatened gull during the non-breeding season in two sites with different anthropogenic influence

Analysis of fatty acid composition can provide information about the effect of anthropogenic activities on the trophic choices of different species, including seabirds. The Olrog’s Gull Larus atlanticus, a threatened species found along the coast of Buenos Aires Province, Argentina, exhibits carcinophagus feeding habits. However, its association with human activities, such as recreational fishing and others, is increasing, particularly during the non-breeding season. During the non-breeding seasons of 2018 and 2019, we analysed the circulating fatty acid composition in Olrog’s gulls from two contrasting sites regarding the level of urbanization and human disturbance: Mar Chiquita, a non-urban site, with low human impact and presence of crab mudflats, and Mar del Plata, an urban site, with high human impact and absence of crab mudflats. Significant differences in fatty acid composition were observed between the two sites that can be related to non-urban and urban diets, and for ‍n-3/n-6 ratio that differentiates aquatic vs. terrestrial diets. Distinct segregation patterns between individuals at each site were observed, resulting in two major groupings: birds sampled at the non-urban site and those at the urban site. However, some birds exhibited mixed patterns, suggesting variability in the consumption of trophic sources. This study contributes to the broader understanding of trophic ecology of seabirds during non-breeding season in environments influenced by anthropogenic activities, employing non-lethal techniques.