When India’s vulture population collapsed, half a million human deaths followed: study

Vultures may not be the most popular animals in the world, but the work they do is essential to human life, a new study finds.

New research attributes the 500,000 human deaths in India over five years in the early 2000s to a decline in the country’s vulture population.

“They serve a very important function in the environment that benefits us as a society and as humans,” said co-author Eyal Frank, an economist at the University of Chicago. As it happens host Nil Köksal. “They clean up a lot of dead animals and disinfect and clean up the area for us.”

Without these sanitation facilities, waterways become polluted and diseases flourish, especially in areas with lots of livestock, according to new research is expected to be published in the journal American Economic Review.

The findings have been praised by conservationists who have long warned about the threats to carrion-eating birds around the world.

What happened to the vultures in India?

India was once home to tens of millions of vultures. But in the mid-1990s, the birds began dying en masse and their populations were reduced to near-extinction levels.

For years, the sudden deaths were a mystery. But in 2004, scientists have solved the case. The birds were poisoned by diclofenac, a nonsteroidal painkiller widely used in cattle and other livestock. Even trace amounts of the drug cause kidney failure in vultures native to Europe, Asia and Africa.

The drug’s patent expired in 1994, and when cheaper generic versions came on the market, Indian farmers began using it to help sick and injured animals recover faster. Then the birds, which feed on livestock carcasses, began dying.

“That made perfect sense to the cattle, the animals and the farmers. What they didn’t know was that vultures were being poisoned unintentionally,” Frank said.

Diclofenac was banned for veterinary use in India in 2006. Conservationists say some farmers and veterinarians still use the drug, or other equally toxic alternatives.

How did the study calculate the death toll?

Frank and his co-author, Anant Sudarshan, an economist at the University of Warwick, estimate that the loss of vultures between 2000 and 2005 led to an additional 100,000 human deaths per year in India, bringing the total to 500,000.

They arrived at this figure by comparing human death rates in India before and after the vulture disaster.

Areas that traditionally had few vultures saw little change, they found. But in places where the birds once thrived, human mortality rose by more than 4 percent. The effect was most dramatic in places with lots of livestock.

The authors also tested the water quality in the areas they studied and found that there were higher levels of pathogens in areas that previously had high vulture populations.

In addition, they tracked sales of rabies vaccines, which rose sharply after the vultures declined. This, Frank said, supports anecdotal evidence that as vultures declined in India, wild dogs — some of which carried rabies — flourished.

“I hope people see this as evidence that the natural world, well-functioning ecosystems and biodiversity can actually have an impact on human well-being,” Frank said.

What do vulture experts say?

Vulture expert Corinne Kendall, who was not involved in the study, warned that studies based on observational data are less powerful than those based on experiments.

Still, Kendall, curator of conservation and research at the North Carolina Zoo, said this study is “a great example of the differences in the effects on human mortality in areas where vultures have disappeared and areas where they have not.”

It also, she says, supports previous research that suggest that vultures play a role in preventing the spread of disease.

Not only do they scavenge animal carcasses, but their highly acidic stomachs can also destroy pathogens, she said, preventing the birds from spreading disease as some other scavengers do.

“This work should be a wake-up call to other areas where vultures are in decline. We need to act now, because the loss of these scavengers could have major consequences for people,” Kendall told CBC in an email.

“Vultures may not be that attractive or cute, but we need them.”

Chris Bowden agrees. He is the vulture programme manager at the UK’s Royal Society for the Protection of Birds and co-chair of the International Union for Conservation of Nature’s vulture specialist group.

He is working with other conservationists and partners in India to restore the vulture population by educating people about safe alternatives to diclofenac, setting up captive breeding programs, and advocating for more rigorous pharmaceutical testing long before veterinary drugs reach the market.

Thanks to these collective efforts, the birds have been saved from extinction, he says.

But, according to India’s State of the Bird Report 2023Four vulture species remain on the critically endangered list, and three species have experienced long-term population declines of 91 to 98 percent.

“I don’t think they’ll ever come back in the same numbers as before,” he said.

Both Kendall and Bowden say vultures face numerous threats worldwide, including hunting, accidental poisoning and collisions with human infrastructure.

Bowden says he knows vultures have “a bit of an image problem,” but he sees them as “magnificent birds of prey that are an amazing part of biodiversity in their own right.”

“We hope that this [study] emphasizes that more clearly so that people take it more seriously and actually do something to protect these fantastic birds,” he said.

Frank hopes his work will highlight the importance of biodiversity.

“It’s important for us … and not just for the vague feelings we have about the more charismatic species that are out there,” he said.