Most plastics consumed by city vultures come directly from food outlets

Since the 1950s, mankind has produced around 8.3 billion tons of plastic, adding another 380 million tons to this amount every year. Only 9% of this is recycled. The inevitable result is that plastic is everywhere, from the depths of the oceans to the summit of Everest – and notoriously, inside the tissues of humans and other organisms.

The long-term effects of ingested plastic on people are not yet known. But in rodents, ingested microplastics can alter the function of the liver, intestines, and exocrine and reproductive organs.

Scavenging birds are particularly at risk of ingesting plastic. For example, vultures in the Western Hemisphere regularly feed on landfills and have been observed quietly picking up synthetic materials such as boat seats, rubber gaskets, and roofs.

Now US researchers have shown that the amount of plastic ingested by black and red-headed vultures can be predicted from their location on suburban and peri-urban maps. It is not only a distinction between the birds of the countryside and those of the city; the amount ingested depends on the local density of human commerce in urbanized landscapes. These findings are published in Frontiers in Ecology and Evolution.

“Here we show that black vultures and red-headed vultures in areas with more urban development and a higher density of commercial food providers ingest more plastic,” said Hannah Partridge, PhD student in the Department of Geography and Earth Sciences from the University of North Carolina. in Charlotte, and the first author of the study.

“It’s possible they ate some of this plastic on purpose rather than exclusively by accident, as is commonly believed.”

Vulture pellets save plastic consumption

In 2021 and 2022, Partridge et al. studied eight communal roosts shared by black and red-headed vultures in the Charlotte metropolitan area (human population of 2.8 million and growing). The lodges generally host between 20 and 500 vultures. Under the perches, they collected a total of 1,087 pellets of undigested material vomited up by the vultures.

Of these pellets, 60% contained plastic, or 2.7% of the total mass on average. Other components included vegetation, earth, rocks, animal remains, metal, cloth, paper, wood, and glass. The authors were able to identify the types of plastic materials using Fourier Transform Infrared (FTIR) spectroscopy. The most commonly found were silicone rubber (7.5% of samples analyzed), high density polyethylene (7.0%), polyethylene (6.4%) and biopolyethylene silicate (5.3%).

The researchers then looked for associations between the amount of plastic in the pellets and four measures of human development at increasing distances – from 400 meters to 20 kilometers in vulture flight – from the roost. These were the density of commercial food providers (from family stores and food trucks to supermarkets and restaurants), the density of livestock and game producers, the amount of land cover developed, and the distance to the nearest landfill.

Turkey Vulture. Photo by Glenn Bush

Food stores and restaurants

Exploratory statistical analyzes showed that the proportion of pellet mass composed of plastic increased sharply with increasing urban land cover and increasing density of food providers within a 20 kilometer radius. From these results and direct observations, the authors concluded that black vultures especially in the Charlotte metropolitan area could primarily ingest plastics directly from dumpsters belonging to food suppliers.

“Black vultures often roost at night on a transmission tower next to a fast-food restaurant and fly directly to the dumpster first thing in the morning,” Partridge observed. “Red-headed vultures do it less often; they prefer more rural areas and natural food sources.

curious birds

But do vultures eat all that plastic on purpose or by accident? The researchers speculated that vultures might often mistake the plastic for nutritious bone fragments, which they would normally get from carrion.

“Vultures are curious and always seek new food sources, so they may ingest plastic thinking it’s food,” Partridge said. “But they can also sometimes ingest plastic intentionally, to collect bulk to help vomit up indigestible parts of carrion like hair.”

So what can we do to prevent plastic from being eaten by vultures and other vulnerable animals?

“Food suppliers such as restaurants and grocery stores can ensure that their trash is properly bagged, that the trash gets to the dumpster, and that the dumpster is closed and secure. We can also work to ban single-use plastics to protect vultures and other species from harm,” advised lead author Dr. Sara Gagné, associate professor in the same department.

Thanks to Frontiers in Ecology and Evolution for providing this news.

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