As a young man in the 1990s, walking to school in New Delhi, Ananth Sudarshan would watch vultures along telephone wires, awaiting the demolition of nearby leather tanning factories. So when the birds started disappearing, he didn’t notice anymore.
Sudharshan, who now researches environmental policy and economics at the University of Warwick in the UK, didn’t realize then but would help discover decades later, the extinction of India’s vultures had far-reaching consequences for humans living alongside them. the birds In just a few years, the species’ disappearance contributed to the deaths of hundreds of thousands of its fellow citizens.
Along with University of Chicago environmental economist Eyal Frank, Sudarshan used his teenage experiences as inspiration. A new study Appearing in the American Economic Review. As in other developing countries, they found, scavengers act as a natural sanitation system for communities with less developed infrastructure than in the US or Europe, helping to control diseases that might otherwise spread through the carcasses they eat.
Outside experts unaffiliated with the study say it will be a classic that will unlock further research into how the loss of critical species can have catastrophic effects on the human populations that depend on them, often in underappreciated ways. The findings should reshape how the public and policymakers relate to the world around us and how we consider the unintended consequences of environmental destruction.
“We’re interconnected with the rest of the natural world,” Frank said. “I think for a lot of people, it’s this hippie, quasi-tree-hugging idea. Converting it into a number and a result that people care about to death changes how people think about this statement: that we are one with nature. What does that actually mean? This is not a spiritual statement. It is a statement about causal processes.”
The human value of India’s extinct vulture
Sudarshan and Frank estimate that from 2000 to 2005, after a rapid die-off of vultures in the 1990s, an additional 500,000 died in India above pre-existing trends. The near-extinction was an unexpected (and long-unknown) byproduct of the country’s farmers introducing a drug to animals that had previously only been prescribed for humans.
Within a few years, 95 percent of the country’s vulture population was wiped out, dropping from a few million to a few thousand. A decade later, researchers discovered that the drug led to kidney failure and death in vultures when they fed on dead cattle that still had it in their systems.
Sudarshan and Frank compared mortality rates in the following years between areas that were formerly home to vulture populations and those that were not, and found that people began to die at higher rates in areas where the birds lived.
In communities that lost vultures, there were an estimated 104,000 additional deaths per year—deaths that could account for the species’ near-extinction—from 2000 to 2005, the years following the dramatic decline that was the focus of Sudarshan and Frank’s study. This adds up to more than half a million deaths over five years, costing India an estimated $69 billion annually.
“I didn’t anticipate the impact would be this big,” Sudarshan said. But when he and Frank realized that diseases could be spread around without vultures by different vectors, Sudarshan realized that the extinction was “the biggest sanitation shock you can imagine, where you don’t have 50 million corpses disposed of every year.”
Keystone animal species are vital to human health
Ecologists and conservationists have long known that certain species—called “keystone” species—play an important role in ecosystems. Scientists suspect that the role of these species is so important that their loss could have life-or-death consequences for humans. That relationship, however, was difficult to prove.
A lot of circumstantial evidence was found. In India, vultures are known to be highly efficient scavengers, consuming almost all carcasses within less than an hour of finding them. Before extirpation, Indian territories that were home to vultures recorded lower baseline mortality rates than those without. After the birds died, people in the affected areas saw more feral dogs and more decomposing carcasses forming in the fields.
Without the vultures consuming them, more dead animals lay around, sometimes ending up in rivers or other bodies of water, contaminating local water supplies. The absence of vultures becomes an opportunity for other scavengers such as rats and dogs. India did not attempt a wild dog census until 2012, well after the study period. But when they did, there were many other animals in the area previously host to vultures, which suggests that dogs may have evolved after birds were eliminated, and Frank argues.
Dogs and rats are less efficient than vultures at completely eliminating flesh from potentially disease-carrying carcasses, creating more opportunities for a person to come into contact with infected remains. They are also more likely to transmit diseases such as anthrax and rabies to humans. Rabies vaccine orders began to increase in the years after the vulture population declined.
“I was surprised it happened so quickly,” Frank said. “We often say that anecdotes are not proof, but the amount of anecdotes about how people were negatively affected by the disappearance of vultures, we read it more and more and said, ‘Well, this is data that’s been shown.’”
Sudarshan and Frank now provide a template for studying the effects of species loss on human health, and researchers unimpressed with the study told me they hope to pursue more such studies. Frank hopes that future work may be able to identify whether specific causes of death increase after the eradication of a keystone species.
Rethinking our relationship with the animals we live alongside
The researchers argue that the findings should inform conservation efforts in other regions, such as sub-Saharan Africa, where vultures play a similar sanitation role. Small investments to support local populations can have big returns. More broadly, supporting species considered ecologically critical, of which vultures are just one, is a wise investment.
It is also clear that farmers and agricultural officials should consider potential ripple effects when administering new drugs to livestock. This is a textbook example of one health, the public health paradigm that says we must protect animal and environmental health to protect human well-being.
The drug in question, diclofenac, was introduced because it was a cheap way to treat fever and inflammation in farm animals. The drug was banned when Indian officials learned of its role in vulture deaths, but by then, the damage was already done.
Vultures remain critically endangered in India, with only a few thousand individuals. Sudarshan and Frank argue that their findings should boost conservation efforts in India, although the vultures’ life cycle will make them difficult to recover: they lay at most one egg a year and take years to reach sexual maturity.
The massive consequences of their near-extinction in India remind us that promoting biodiversity means embracing every species, not just the ones that look good on a T-shirt; They and we are all part of a whole.
“We really need to remember these connections. They are very important,” Andrea Santangeli, a conservation scientist at the Center for Environmental Change Research at the University of Helsinki, told me. “We cannot live a healthy life without a healthy nature.”
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