Contrasting patterns of plastic ingestion and transport by an opportunistic gull across urban and agricultural landscapes

Over the past few decades, plastic production has increased significantly globally. These anthropogenic materials often enter terrestrial and marine ecosystems via various pathways. Recent studies highlight that seabird species, in special the opportunistic ones such as the yellow-legged gull (Larus michahellis), can act as biovectors, transporting plastic debris from landfills to protected or sensitive habitats, facilitating plastic leakage across ecosystems. However, the influence of plastic availability on the intensity and patterns of this biovectoring role has not yet been properly quantified. Here, we aimed to investigate the differences in the abundance and types of plastics ingested and transported by yellow-legged gulls from two colonies situated in contrasting human-related environments: a coastal urban city (Barcelona, Spain) and an inland agricultural area (Ivars Lake, Spain). We found plastics in 100% of pellets from the urban colony and in 56% from the inland colony, with higher plastic diversity and quantity in the urban population. By combining plastic analysis from pellets with GPS tracking data of 27 breeding yellow-legged gulls, we investigated how differences in the habitat use between both environments affect plastic exposure. Urban gulls were estimated to transport roughly ten times more plastic to their breeding area compared with the inland breeding gulls. These results highlight the important role of the coastal urban population as a biovector of plastics from the polluted habitats to the colonies.