Microplastic ingestion and diet analysis in migratory shorebirds at Bahía Lomas Ramsar site, Chile

Microplastic (MP) pollution is an emerging threat to marine and coastal ecosystems and their fauna, even in remote and protected areas. Shorebirds depend on wetlands and feed mainly on benthic invertebrates, making them vulnerable to contaminants that accumulate in sediments and their prey. Stable isotope analysis provides a useful framework to interpret MP ingestion in relation to trophic ecology. We applied stable isotopes of carbon (δ13C) and nitrogen (δ15N) to investigate the diet of three migratory shorebirds: the Two-banded Plover (Anarhynchus falklandicus), the Magellanic Oystercatcher (Haematopus leucopodus), and the Hudsonian Godwit (Limosa haemastica) at Bahía Lomas (Tierra del Fuego, Chile), and we quantified MP ingestion. Stable isotope analyses revealed that the Two-banded Plover exhibited a larger and differentiated isotopic niche respect to the other two species, whose niche widths were similar and showed substantial overlap. Mixing models indicated a greater dietary contribution of biofilm for Two-banded Plover, suggesting feeding at lower trophic levels and a stronger association with surface sediments. MPs were detected in sediments, macroinvertebrate prey, and fecal samples of all species, but MP contamination was higher in Two-banded Plover. This difference may be associated with its greater proportional reliance on biofilm. However, this exposure pathway remains hypothetical, as MPs were not directly quantified in biofilm. All detected MPs were fibres, predominantly blue, with polyethylene the most frequent polymer. We provide the first evidence of MP contamination in shorebirds and their trophic resources at Bahia Lomas and anywhere in Chile, illustrating how plastic pollution impacts remote and protected wetlands.