Abstract
Among the various types of pollution, anthropogenic debris such as plastics has become a major source of concern for the functioning of ecosystems and the health of the organisms living there. The main aim of this thesis was to quantify and characterize exposure to anthropogenic debris, including plastics, in Yellow-legged Gulls Larus michahellis in the western Mediterranean basin, in order to better understand its impact on the health, reproductive success and population dynamics of seabirds. We examined this question through three approaches: 1) the study of the variation in exposure within a colony during the breeding period; 2) the study of the spatial and temporal variability of exposure between colonies on a basin-wide scale; 3) and finally, the quantification of plastics in the birds' digestive tracts. The latter required the development of a new protocol for quantifying microplastics (10μm to 1mm) in vertebrate tissues. While the general dependence of gulls on anthropogenic waste was underlined by our results, variation in exposure was observed both during the breeding season and according to the colonies studied. This variation seems to be mainly due to the number of dumps and the percentage of agricultural cover around the colonies. While only a few individuals retained plastics larger than 1 mm in their digestive tract at the time of death, almost all had small microplastics. A total average of 39.25 (± 30.60) mg of plastic was found in the gulls' digestive tracts, including 8.45 (± 5.24) mg of small microplastics. The work presented in this thesis represents one of the first efforts to quantify and qualify the exposure of Mediterranean birds to plastics and other waste. Nevertheless, much still remains to be done to understand the impact of this pollution on individual health, its link with other stressors such as parasites, and the role of gulls in the wider-scale dissemination of this pollution.