Vultures fight climate change, one carcass at a time

Vultures have a face only a mother could love, but their unsavory eating habits minimize greenhouse gas emissions globally. Featured image source: Wikimedia Commons

Reference: Plaza, PI., Lambertucci, SA. 2022. Mitigating GHG emissions: a global ecosystem service provided by obligate scavenging birds. Ecosystem Services 56.

I’ll level with you, dear reader– vultures are probably not your favorite bird. They’ve got a face only a mother could love, one that spends most of its time buried in dead meat. While some birds might take a peaceful dip in your bird bath to stay cool, vultures defecate on their legs, and in lieu of birdsong, they can only hiss and grunt. Despite these quirks, there is plenty to appreciate about these bald birds. Researchers recently identified an unsung but critical role vultures play in the environment: reducing greenhouse gas emissions.

Vultures at play

When an animal dies in the wild and there are no scavengers around to eat what remains, bacteria in the environment slowly decompose its body. Just as humans exhale carbon dioxide, these bacteria release carbon dioxide as they work. When viewed at a global scale, this decomposition represents a significant source of greenhouse gases: up to 13 Tg of carbon dioxide, nitrous oxide, and methane are released by bacteria as they recycle the energy stored in animal tissue.

Luckily for us, scavenger animals like vultures make a living off freshly deceased animals. Vultures are obligate scavengers, meaning they get all of their energy from finding and consuming dead meat. Their anatomy is optimized for the task: unlike most other birds, they have both great vision and a strong sense of smell, allowing them to identify a fresh carcass from great distances. They ride on thermals, traveling large distances efficiently during their search. That nose-turning habit of leg-defecation doesn’t just them cool; it also contains a concentrated uric acid that kills pathogens they come in contact with while eating decomposing flesh. Their highly acidic stomach further suppresses the risk of disease. These factors and more make them very successful scavengers, and the animal that has the greatest potential to reduce natural decomposition– and therefore, reduce greenhouse gases from the process.

Livestock sometimes die in the field of natural causes and many animals are killed by vehicle traffic; in both of these instances, it falls on us to clean up the mess when scavengers aren’t around. Disposal methods include composting, anaerobic digestion, rendering, or natural decomposition (letting the body decompose in nature). These methods are costly and can release additional greenhouse gases– up to 60 Tg per year, according to the scientists studying vultures and carbon emissions.

The white-rumped vulture, one of the vulture species at risk of extinction in India. Image source: Wikimedia Commons
Vultures at risk

The role vultures play in mitigating greenhouse gas emissions is an ecosystem service, but the decline of vulture populations around the globe threatens not only their populations but also the benefits to humans and nature they provide. When researchers estimated the greenhouse gas emission reduction potential for 21 of the 22 vulture species (the odd one out, the palm-nut vulture, keeps a vegetarian diet), they found almost 98% of reduction potential comes from the three most common species. This isn’t to say that only three vulture species are up to the task; rather, the three most common species are the only ones whose populations have not been so diminished that they can no longer fulfill their ecological role. The white-backed vulture, for example, has lost 99.9% of its population due to pesticide application in its native India, which contaminates the carcasses it eats. Vulture populations in Africa have decreased by 62% on average, with some species down up to 80%.

While the ecosystem services we may obtain through healthy vulture populations are worth accounting for, the loss is more obvious in the disruption of their ecological role. Regions that have lost their vultures have an evident breakdown in the cycle of life– less carrion eaten means organisms are left to rot and less energy is cycled through the food web.

Vultures have long been maligned as pests and harbingers of disease, but one only needs to take a step back to see how important these animals are for humans and nature. Regions are starting to take note, and conservation efforts are under way to bring vulnerable vultures back from the brink. These efforts may one day result in fewer greenhouse gas emissions as vultures regain their ecological niche, but the greater benefit will be self-evident: rare birds soaring once again in their natural home in the great web of life.

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