Black vulture, Coragyps atratus
Newswise — Since the 1950s, humanity has generated an astonishing 8.3 billion tons of plastic, with an additional 380 million tons added each year. Shockingly, only 9% of this vast amount is recycled. Consequently, plastic has pervaded every corner of the Earth, from the ocean depths to the peak of Mount Everest, and alarmingly, it has even made its way into the tissues of humans and other organisms, becoming a notorious global concern.
The lasting impact of plastic ingestion on human health remains uncertain. However, studies on rodents have shown that microplastics consumed orally can negatively impact the liver, intestines, as well as exocrine and reproductive organs, raising concerns about potential long-term effects in humans.
Scavenging birds, such as New World vultures, are particularly vulnerable to ingesting plastic. These birds often frequent landfills as a food source and have been observed leisurely pecking at synthetic materials, including boat seats, rubber seals, or roofs, among others, putting them at heightened risk of plastic ingestion. This highlights the dire consequences of plastic pollution on wildlife, even in unexpected and remote locations.
Researchers in the United States have recently discovered that the quantity of plastic ingested by black vultures (Coragyps atratus) and turkey vultures (Cathartes aura) can be predicted based on their location on maps of suburban and exurban areas. Interestingly, this distinction is not simply between birds in urban versus rural areas, but rather depends on the density of human commerce within the urbanized landscapes. These findings, which have been published in Frontiers in Ecology and Evolution, shed light on the complex relationship between vulture behavior and plastic ingestion, revealing the significant impact of human activity on wildlife and plastic pollution in the environment.
Hannah Partridge, a doctoral student at the Department of Geography and Earth Sciences of the University of North Carolina at Charlotte, and the first author of the study, stated, "Here we show that black vultures and turkey vultures in areas with more urban development and a greater density of commercial food providers ingest more plastic." This significant finding underscores the link between plastic ingestion by vultures and the level of urbanization, as well as the density of human-related food sources, providing further evidence of the intricate relationship between human activities, urban landscapes, and plastic pollution impacting wildlife.
“It’s possible that they eat some of this plastic on purpose rather than exclusively by accident, as is typically believed.”
Vulture pellets record plastic consumption
In the years 2021 and 2022, Partridge et al. conducted a study on eight communal roosts that are inhabited by both black and turkey vultures in the rapidly growing Charlotte Metropolitan Area, with a human population of 2.8 million. These roosts are known to accommodate varying numbers of vultures, ranging from 20 to 500 individuals. As part of the study, researchers collected a total of 1,087 undigested material pellets that were regurgitated by the vultures from underneath these roosts. These pellets serve as important indicators of vulture feeding behavior and provide valuable data for understanding the extent of plastic ingestion by these birds in the urban environment.
The study revealed that out of the collected pellets, a staggering 60% contained plastic, which on average made up 2.7% of the total mass. Along with plastic, the pellets also contained various other components, including vegetation, dirt, rocks, animal remains, metal, fabric, paper, wood, and glass. The researchers utilized Fourier transform infrared (FTIR) spectroscopy to identify the types of plastic materials present in the pellets. The most commonly identified types of plastic were silicone rubber, accounting for 7.5% of the samples analyzed, followed by high density polyethylene at 7.0%, polyethylene at 6.4%, and silicate bio polyethylene at 5.3%. These findings provide crucial insights into the specific types of plastic materials that vultures are ingesting in urban areas, shedding light on the potential sources and composition of plastic pollution impacting these birds.
The researchers conducted further analysis to investigate potential associations between the amount of plastic found in the vulture pellets and four measures of human development. These measures were examined at increasing distances, ranging from 400 meters to 20 kilometers in radial distance from the roost, as the vulture flies. The four measures of human development included the density of commercial food providers, which encompassed a range of establishments from small local stores and food trucks to larger supermarkets and restaurants. The density of livestock and game producers, the extent of developed land cover, and the proximity to the nearest landfill were also considered in the analysis. By examining these variables, the researchers aimed to understand how human activities and urbanization may be correlated with the ingestion of plastic by vultures in the study area.
Food stores and restaurants
The exploratory statistical analyses conducted by the researchers revealed a notable correlation between the proportion of pellet mass composed of plastic and two factors: increasing urban land cover and increasing density of food providers within a 20-kilometer radius from the roost. Based on these findings, along with direct observations, the authors concluded that black vultures in the Charlotte Metropolitan Area may be primarily ingesting plastics directly from dumpsters associated with food providers. This suggests that the availability of food from commercial sources, such as supermarkets, restaurants, and food trucks, may play a significant role in the ingestion of plastic by vultures in urban areas. The results highlight the potential impact of human activities and urbanization on the ingestion of plastic by wildlife, specifically scavenging birds like black vultures.
Partridge further observed that black vultures, in particular, have a tendency to roost overnight on transmission towers located near fast food restaurants and then head straight to the dumpsters of these establishments early in the morning. On the other hand, turkey vultures exhibit this behavior less frequently, as they generally prefer rural areas and natural food sources. These behavioral differences may explain the higher ingestion of plastic by black vultures in urban areas compared to turkey vultures in more rural areas, as the availability of food from commercial sources could be a significant contributing factor to their plastic consumption patterns.
Curious birds
But do the vultures eat all this plastic on purpose or by accident? The researchers hypothesized that vultures may commonly mistake plastic for nutritious bone fragments, which they would normally get from carrion.
“Vultures are curious and always looking for new food sources, so they may ingest plastic thinking it’s food,” said Partridge. “But they may 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?
Dr. Sara Gagné, the senior author of the study, recommended several measures that food providers such as restaurants and grocery stores can take to reduce the ingestion of plastic by vultures and other wildlife. These include properly bagging and disposing of trash in dumpsters, ensuring that dumpsters are closed and secured to prevent access by scavengers, and working towards banning single-use plastics to prevent environmental pollution. These proactive steps can help protect vultures and other species from harm caused by ingesting plastic. It underscores the importance of responsible waste management practices and reducing the use of plastic to mitigate the impacts of plastic pollution on wildlife and ecosystems.
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