Storks and gulls transport hundreds of kilos of plastic from landfills to wetlands in southwest Spain
Estimates reveal that the lesser black-backed gull transport up to 285 kg per year, followed by the yellow-legged gull with 160 kg, and the white stork with 86 kg — with significant consequences for natural ecosystems.
White storks at a landfill in western Andalusia. Credit: Enrique García Muñoz / FotoConCiencia. CC BY-ND license
Plastic pollution is one of the main environmental problemas threatening threats to aquatic ecosystems. A new study from the Doñana Biological Station (EBD-CSIC), conducted in the Bay of Cádiz in southwest Spain reveals differences between several aquatic birds that act as plastic biovectors, —organisms capable of transporting these pollutants from areas of high concentration, such as landfills, to natural protected areas where plastics are scarce. The inadequate management of waste promotes the transfer of plastics from landfills to natural ecosystems through the movements of these birds, increasing the dispersion of these pollutants.
Three species with differences
This pioneering comparative study examined the role of three waterbird species from the Bay of Cádiz that frequently visit nearby landfills: the white stork (Ciconia ciconia), the lesser black-backed gull (Larus fuscus), and the yellow-legged gull (Larus michahellis).
To do this, the team combined GPS tracking, landfill census data, analysis of pellets (regurgitations), and Fourier-transform infrared spectroscopy (FTIR) to determine the quantity and type of plastic transported by each species from the same source.
“Our study shows not only that all three species are important plastic biovectors from landfills to wetlands, but also that there are notable differences between them,” explains Julián Cano, PhD researcher at the Doñana Biological Station – CSIC and lead author of the paper.
The white stork, being the largest of the three, carries the highest amount of plastic per individual, as it produces larger pellets, though the percentage of plastic is similar to that found in the gulls. Overall, all three species mainly transport hard plastic fragments. However, when analyzed separately, key differences emerge: storks primarily carry small, hard plastic fragments and silicone rubbers — a type of waste they may mistake for worms — which are absent in the other two species. In contrast, both gull species tend to transport larger pieces of plastic and more frequently carry film-type plastics, such as packaging and wrappers.
The lesser black-backed gull population: the main carrier
While the white stork carries more plastic per individual, population-level estimates reveal clearer differences among species. Based on 2022 landfill censuses and GPS movement data, the researchers estimated that the lesser black-backed gull was the main transporter of plastics to the Bay of Cádiz, largely due to its abundance, with around 285 kg per year, followed by the yellow-legged gull with 160 kg, and the white stork with 86 kg.
“In the case of the yellow-legged gull, a resident species in the Bay of Cádiz, this transport remains fairly constant throughout the year,” says Cano. “In contrast, the other two species mainly do so at specific times of the year: the lesser black-backed gull during winter, and the white stork during its spring and autumn migrations between Spain and Morocco, when their numbers at the landfill peak.”
Using GPS data, the team also identified which parts of the Bay of Cádiz marshes are most likely to be affected by this plastic transport, depending on the distribution of each species. The yellow-legged gull spends most of its time near its breeding colonies, the stork remains close to the landfill, and the lesser black-backed gull is more widely distributed across the bay.
A problem tied to our consumption habits
The effects of plastics on living organisms are highly variable, affecting both the individual birds that transport them and the ecosystems as a whole.
“A particular concern is that smaller plastics can enter the food chain through filter-feeding invertebrates,” explains Andy J. Green, research professor at the Doñana Biological Station (CSIC). “Moreover, organisms exposed to this pollution can suffer not only from the plastics themselves but also from their chemical additives, which can be even more hazardous. These effects can include choking or internal injuries from larger pieces, as well as toxic, reproductive, or endocrine disorders.”
The study’s findings highlight the importance of understanding how plastics move from landfills into natural ecosystems. Each species may carry different types of plastics, do so at different times, or originate from different sites. Studying all of them is essential to better understand this process—known as biovectoring—and to design effective mitigation strategies.
“Preventing birds from visiting landfills is not easy. This issue is closely linked to our throwaway consumption model and poor waste management,” concludes Julián Cano. “Better waste separation, improved recycling, and, above all, reducing plastic consumption are key to preventing these materials from ending up in protected natural areas.”
Reference
Julián Cano-Povedano, Cosme López-Calderón, Francisco Hortas, Victor Martín-Vélez, Marta I. Sánchez, Belén Cañuelo-Jurado, Andrés Cózar, Judy Shamoun-Baranes, Wendt Müller, Chris B. Thaxter, Luc Lens, Eric Stienen, Manuela G. Forero, Isabel Afán, Julio Blas, Wolfgang Fiedler, Andy J. Green. Spatiotemporal differences in plastic biovectoring among three sympatric waterbirds. Environmental Research. https://doi.org/10.1016/j.envres.2025.122477