As India’s vultures face extinction, so too do human deaths

As a young man on his way to school in New Delhi in the 1990s, Anant Sudarshan often saw vultures perched on telephone wires, waiting for waste from a nearby tanneries. So when the vultures began to disappear, he couldn’t help but take notice.

Sudarshan, who now studies environmental policy and economics at the University of Warwick in the UK, didn’t realise it at the time, but would discover decades later, that the extinction of the Indian vulture had far-reaching consequences for the humans who lived alongside these birds. The disappearance of the species killed hundreds of thousands of its fellow vultures in just a few years.

Sudarshan teamed up with University of Chicago environmental economist Eyal Frank and drew inspiration from his own teenage experiences. A new study The study, published in the American Economic Review, found that, as in other developing countries, in communities where infrastructure is less developed than in the United States or Europe, scavengers act as a natural sanitation system, helping to control diseases that might be spread through the carcasses they eat.

Outside experts not affiliated with the study say it will be a classic that will kick off further research into how the loss of keystone species can have catastrophic effects on the human populations that depend on them in ways that are often underestimated. The findings should reshape the way the public and policymakers relate to the world around us and how we think about the unforeseen consequences of ecological damage.

“We are interconnected with the rest of the natural world,” Frank said. “I think for a lot of people it’s a hippie, tree-lover kind of concept. Translating it into numbers and outcomes that people care about, like mortality, really changes how people think about this statement: We are one with nature. What does that really mean? It’s not a spiritual statement. It’s a statement about cause and effect mechanisms.”

Sudarshan and Frank estimate that half a million more people died in India from 2000 to 2005 than before, due to the rapid extinction of vultures in the 1990s, an unintended (and long-unknown) byproduct of farmers in that country introducing a drug to their livestock that had previously been used only on humans.

Within a few years, 95% of the country’s vulture population was wiped out, from tens of millions to a few thousand. A decade later, researchers discovered that the drug caused kidney failure and death in vultures when they ate dead livestock that still had the drug in their systems.

Sudarshan and Frank compared mortality rates in areas that were once vulture habitat with those in areas that were not vulture habitat in the years after the vultures died, and found that human mortality rates began to be higher in areas where the vultures once lived.

In communities where vultures have disappeared, an estimated 104,000 vultures die each year, deaths that may be attributed to vulture extinction. Vulture populations fell dramatically between 2000 and 2005, the focus of Sudarshan and Frank’s study. Over five years, the death toll totaled more than 500,000 vultures, costing India an estimated $69 billion a year.

“I didn’t expect the impact would be this big,” Sudarshan said. But when he and Frank realized that without vultures, diseases could be spread through various vectors, Sudarshan realized that vulture extinction was “the biggest health shock you can imagine, 50 million carcasses a year that are not being processed.”

Ecologists and conservationists have long known that some species, called “keystone” species, play critical roles in ecosystems. Scientists have also suspected that these species’ roles are so important that their disappearance could have life-or-death consequences for humans. However, this relationship has been difficult to prove.

There is plenty of indirect evidence. In India, vultures are extremely efficient scavengers, eating almost all carcasses within an hour of discovering them. Before the extinction, areas of India with vultures already had lower mortality rates than areas without them. After the vultures went extinct, people in affected areas reported seeing more feral dogs and more rotting carcasses piling up in fields.

Without vultures to prey on them, there are more dead animals, which sometimes end up in rivers or other bodies of water, contaminating local water sources. The disappearance of vultures creates opportunities for other scavengers, such as rats and dogs. India didn’t conduct a census of wild dogs until 2012, well after the study period. But when they did, they found an increase in wild dog populations in areas that were previously hospitable to vultures, which Sudarshan and Frank believe means that wild dogs may have thrived after the vultures were eliminated.

Compared to vultures, dogs and rats are less efficient at completely removing the flesh from carcasses that may carry disease, creating more opportunities for people to come into contact with infected carcasses. They are also more likely to transmit diseases such as anthrax and rabies to people. In the years following the dramatic decline in vulture numbers, orders for rabies vaccines began to increase.

“I was struck by how suddenly and how quickly this happened,” Frank said. “We always say anecdotes are not evidence, but the more anecdotes there were about how people were negatively impacted by the loss of vultures, the more we read them and said, ‘Well, this has to show up in the data.’”

Sudarshan and Frank have now provided a template for studying the effects of species extinction on human health, and researchers unaffiliated with the study told me that they look forward to more such studies. Frank hopes that future studies will determine whether specific causes of death increase after keystone species go extinct.

The researchers believe the findings should inform conservation efforts in other regions, such as sub-Saharan Africa, where vultures play a similar hygienic role. Small investments to support local populations could yield large returns. More broadly, supporting species considered ecologically critical is a smart investment, and vultures are just one of them.

Clearly, farmers and agricultural officials should consider potential knock-on effects when giving new drugs to livestock. It’s a classic example of “One Health,” the public health approach that holds that we should protect animal and environmental health in order to protect human well-being.

The drug in question, diclofenac, was introduced to India as a cheap treatment for fever and inflammation in farm animals. Once Indian officials learned of its role in the vulture die-offs, they banned its use, but by then the damage had been done.

Vultures remain critically endangered in India, with only a few thousand left. Sudarshan and Frank think their findings should encourage conservation efforts in India, though the vultures’ life cycle will make them difficult to recover: They lay no more than one egg a year and take years to reach sexual maturity.

The dramatic consequences of their extinction in India remind us that promoting biodiversity means including every species, not just those that look good on a T-shirt; they are part of the same whole that we are.

“We need to really remember these connections,” Andrea Santangeli, a conservation scientist at the University of Helsinki’s Ecological Change Research Center, told me. “They are vital. We cannot have healthy lives without healthy nature.”

A version of this article originally appeared on Future Perfect communication. Register Here!