Hungry seagulls don’t just steal chips and sandwiches. They learn our habits and look for reliable food sources. This includes waste processing centres, landfills or areas where food waste is concentrated. To take advantage of these food sources, many gull populations have moved inland from the coast.
Seagulls and other birds can feed wherever our waste is disposed of. At the landfill, seagulls eat the waste before it can be covered up. If the pieces of plastic or glass covered in food are small enough, gulls will swallow them whole. Only the food itself is digested, and when the gulls return to roost, the waste flows back up and contaminates the area. This transfer of contaminants is known as “biovectoring.”
Scientists like me are quantifying for the first time how much plastic and other waste is flowing into important natural areas through the daily movements of birds.
Many herring gulls that breed in the UK and other parts of northern Europe migrate to Andalusia in southern Spain, where they form overwintering populations of more than 100,000 birds, feeding mainly on rice fields and reclaimed land. Fortunately, many of these birds are fitted with GPS tags while breeding. This allows detailed tracking of movements.
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Malaga’s Fuente de Piedra Lake is a migration hotspot for herring gulls. This wetland is of special natural importance and has been designated as a Site of International Importance under the World Convention known as Ramsar. It is most famous as Spain’s largest flamingo breeding ground. Seagulls fly up to 80 miles to the landfill to feed, then return to roost.
By combining GPS data, waterfowl counts and analysis of regurgitated pellets, scientists estimate that the gulls deposit an average of 400kg of plastic, plus more than two tonnes of other debris such as glass, textiles and pottery, into the lake each year. This lake has a high salt content as there is no runoff, making it friendly to flamingos. The imported plastic remains in the lake and breaks down into microplastics. Can be ingested by flamingo chicks, aquatic insects, and other animals.
Two northern gulls chase a stork that is carrying plastic it has picked up from a landfill in its beak.
Enrique García Muñoz (FotoConCiencia)CC BY-NC-ND
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On the Andalusian coast, these gulls join a mix of the resident yellow-backed gull (equivalent to the herring gull), migratory and resident storks as the three main waterbirds that visit reclaimed sites.
In the wetlands of the Bay of Cadiz (another Ramsar wetland) that surround the historic city, which is now a favorite port of call for cruise ships, three species combine to spread different types and sizes of plastic into different microhabitats. Every year, 530kg of plastic is deposited in wetlands by recycled pellets. Because of their larger size, storks carry more waste per bird, but most of the plastic is transported back by the smaller black-headed gulls, which overwinter there in large quantities.
Plastic film spewed out by seagulls roosting in fields in Atherton, Greater Manchester.
Kane BridesCC BY-NC-ND
The ingestion of this waste has strong effects on the birds themselves, including through direct mortality from disease, suffocation and entanglement in plastic, and the toxic effects of additives in the birds. After being regurgitated as pellets, those plastics pose a threat to all fauna and easily enter our food supply through aquaculture and salt production, which is important in the Gulf of Cadiz.
These studies conducted in Spain address issues that are ongoing across Europe. There are no comparable quantitative studies in the UK yet, but similar problems occur wherever seagulls are concentrated to feed on our waste. In the future, if storks become abundant in the UK, they will visit landfills along with gulls and perhaps cattle egrets.
The closure of many landfill sites and improved waste management may be contributing to the recent decline in many gull populations in the UK and elsewhere. However, as long as consumer society produces large amounts of waste, this problem of plastic leakage will continue. Reducing waste and reusing things is better than recycling. One reason for this is that food containers can be eaten by birds before they can be recycled. Cleaning food containers before putting them in the trash and composting your own food waste can also help reduce this phenomenon.
