Research review: study demonstrates how plastic ingestion by vultures may cause wider impacts

Black Vultures feeding in a rubbish dump/ illustrative (c) Katja Schulz/ Creative Commons
Black Vultures feeding in a rubbish dump/ illustrative (c) Katja Schulz/ Creative Commons

It is widely known that plastic is a pollutant that can adversely affect wildlife, people and whole ecosystems. When it comes to vultures, little is known about how plastic ingestion impacts these birds or their role in dispersing plastic debris across the wider environment. A recently published research article investigates these issues using Andean Condors, Black Vultures and Turkey Vultures in Northwestern Argentine Patagonia, and determined that in some cases they do transport plastic waste to more remote areas, causing local pollution.

 

Overview

Today, huge amounts of plastic waste are generated and discarded daily. This issue raises concerns since plastic debris remains in the environment from hundreds to thousands of years and can cause adverse impacts on natural habitats and subsequently on biodiversity. Plastic waste is usually abundant in rubbish dumps that provide food sources for several animal species, including vultures. When organic items are mixed with plastic and are ingested, it poses a real risk to animals. Not only can this create health problems to animals, but plastic waste can also be transported and dispersed by animals to sites far away. 

 

Some vulture species, as obligate scavengers, regularly visit rubbish dumps to find food. Feeding on organic waste but also synthetic material has produced several impacts on them, varying from nutritional problems to infections and metabolic alterations. Part of the plastic debris ingested is then regurgitated in their pellets, which, since vultures can travel vast distances daily, may cause dispersal of ingested plastic debris to remote areas that would otherwise have low levels of plastic pollution. This study aimed to understand the effects of rubbish dumps on plastic consumption by vultures and the dispersal of plastics to natural environments mediated by bird transport with Patagonian vulture species by tracking and evaluating different factors such as feeding habits and use of sites close to human activity. 

 

Method

The researchers conducted the study in Northwestern Argentine Patagonia. This relatively pristine area hosts diverse human settlements, which produce large amounts of waste, both organic and synthetic material, disposed at open rubbish dumps that are poorly managed and visited by various animals including vultures. 

 

The research used three vulture species found in the Americas — the Andean Condor, the Black Vulture and the Turkey Vulture.

 

The field team collected fresh pellets from the ground under communal roosts of each species to analyze plastic debris and other synthetic materials. In total, the researchers analyzed 1170 pellets collected from 2010 to 2020: 187 from Andean Condors, 865 from Black Vultures and 118 from Turkey Vultures. 

 

Results

The analysis detected that 17.4 % (203/1170) of material present in the pellets was synthetic, of which 89.2 % corresponded to plastic debris and 10.8 % to other synthetic materials such as paperboard, foil paper, glass, and cloth fragments. 

 

Plastic debris in pellets of Andean Condors was lower at 1.1 % compared to Black Vultures at 17.3% and Turkey Vultures at 24.5 %. The only type of plastic found in condors was ear tags used for livestock practices. This was most likely because Condors generally spend less time foraging close to human settlements compared to the other species, preferring to forage for wild or domestic ungulate carcasses on grazing land.  

 

In addition, the probability of plastic debris occurrence in pellets at roosting sites near rubbish dumps was higher than in those collected far away. However, the research team found plastic debris in pellets up to 56 km away from the nearest rubbish dump, and on an island within a national park where there is no human presence, confirming that vultures play a role in transporting plastic through the wider landscape. 

 

The research team also detected that pellets sampled in 2020 showed a higher presence of plastic debris compared with 2010, confirming increased consumption of plastic by vultures over time.  

 

Conclusions and recommendations

Unfortunately, vultures increasingly ingest plastic worldwide according to reports. In the case of the Critically Endangered California Condor, for instance, waste ingestion is considered the most significant cause of death in nestlings. Plastic ingestion may lead to negative physiological impacts to vultures, although this issue is still not fully understood and merits more attention, especially for the vulture species that forage close to urban areas. 

 

The increase in the occurrence of plastic debris in Black Vulture pellets from 2010-2020 is worrying, and it is probably related to the rise of urbanization and human population in Patagonia. It seems that rubbish dumps are most likely the primary source of plastic for vultures, and in the study area, the majority are open with poor waste management. Better waste management is crucial to avoid the ingestion of plastic and harmful material by vultures and other animals.  

 

The research demonstrates that vultures may disperse plastic from urban sites to the wider landscape, leading to plastic pollution in remote areas. The extent of this likely varies with each species' feeding habits and tolerance to and use of anthropized sites. This issue needs to be investigated further to find solutions to reduce the exposure of wildlife and the wider environment to plastic. 

 

More about the species used in this study

Andean Condors mainly feed on large carcasses and tend to avoid anthropized sites in the study area except for central Chile where the species takes advantage of urban places for food such as rubbish dumps. This species can travel approximately 350 km per day, visiting its established foraging areas and roosting communally in large cliffs generally far from anthropized areas.

 

Black Vultures feed on carcasses of different species and consume human waste discarded in rubbish dumps or the wider landscape, particularly in areas where they roost near human settlements. On average, their home range is around 32 km2, but some may travel more than 50 km from urban to more remote areas. The species moves between their roosting site and their food sources, adjusting their roosting sites according to food availability. It roosts on trees, pylons, high buildings, or low cliffs, with hundreds of individuals typically roosting together.

 

Turkey Vultures inhabit a wide variety of habitats, from deserts to forests, locating carrion due to a well-developed sense of smell and sight. The Turkey Vulture has a more diverse diet compared to the other two species studied, feeding on large ungulates to reptiles, birds and carnivores. Even though in the study area, they have not been observed feeding at rubbish dumps, this species has been reported consuming organic waste in other parts of America. Their movement patterns (excluding migration) are similar to black vultures but have a larger home range of around 60km2. Hundreds of individuals roost together in high trees or buildings.

 

In Europe, and Spain in particular, it is well known that vultures and other scavengers feed in large numbers at some open rubbish dumps, and recent studies have shown that this may expose them to harmful pollutants. This potential threat, therefore, requires further monitoring and research, and waste management strategies should be adapted accordingly.

 

Source

Ballejo F, Plaza P, Speziale K, Lambertucci A, Lambertucci S. Plastic ingestion and dispersion by vultures may produce plastic islands in natural areas. Science of The Total Environment. 2020;755:142421. doi:10.1016/j.scitotenv.2020.142421  

 

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