In the early 1980s, three species of Gyps vulture had a combined population across South Asia estimated at around 40 million birds. By 2017 the estimate for those same three species was about 19,000.
Not thousands lost. Not a decline. Effectively all of them.
The cause was not hunting, or habitat loss, or anything anybody set out to do. It was an anti-inflammatory drug given to cattle to help them work through pain. It took years to work that out, and by the time anyone did, the birds were essentially gone.
Which birds, and how far they fell
Three species took the worst of it. The white-rumped vulture, Gyps bengalensis, was once thought to be among the most abundant large birds of prey anywhere on the planet. It fell by an estimated 99.9 per cent in India between 1992 and 2007. For part of that stretch, from 2001 to 2007, it was losing around 48 per cent of its remaining population every year.
The Indian or long-billed vulture, Gyps indicus, and the slender-billed vulture, Gyps tenuirostris, each dropped by about 97 per cent over the same window, at roughly 22 per cent a year. All three were listed by the IUCN as Critically Endangered, the long-billed vulture from 2002.
Those percentages are worth sitting with, because a 97 per cent decline sounds like the smaller number next to 99.9. It is not. What separates them is how many are left at the end.
The sick birds at Bharatpur
The first person to put a number on what was happening was Vibhu Prakash of the Bombay Natural History Society, who had been studying raptors at Keoladeo National Park in Bharatpur. In 1987 and 1988 he counted 353 nesting pairs of vultures inside the park's 29 square kilometres. By 1996 that count had roughly halved.
What he was finding alongside the empty nests was stranger. Vultures sitting with their necks drooping, listless, sometimes for weeks. Birds dead in the trees and dead in the nests. Post mortems showed chalky white deposits coating the internal organs, which is visceral gout, the sign of kidney failure.
Knowing the birds were dying of renal failure did not explain why. A pesticide was suspected. So was an unknown virus, which was the leading theory for a while, and a frightening one, because a virus sweeping through a continent's vultures is not something anyone can switch off.
The answer came out of Pakistan. A team led by the veterinary scientist J. Lindsay Oaks published in Nature in February 2004, having tracked colonies of white-backed vultures and tested the bodies. The birds dying of renal failure and visceral gout had residues of diclofenac in their tissues. The ones that died of other causes did not. The team then confirmed it directly, reproducing the same kidney damage in vultures exposed to the drug and in vultures fed meat from diclofenac-treated livestock. Later the same year, a separate analysis in the Journal of Applied Ecology showed the same pattern held across the subcontinent.
How a cow's painkiller emptied the sky
Diclofenac is an ordinary non-steroidal anti-inflammatory. Its patent expired in the mid-1990s, cheap generic versions reached Indian markets, and it became a routine treatment for working cattle: an animal that is lame or feverish gets a dose and keeps going. Nothing about that is sinister. It is a farmer looking after an animal they depend on.
The problem is what happens next. India does not generally eat its cattle, so when one dies it is put out, and for centuries what came for it was vultures. If the animal had been treated with diclofenac shortly before it died, the residue was still in the carcass. A vulture that ate it would be dead of kidney failure within days.
The part that is genuinely hard to believe is how little contamination it took.
Modelling by Rhys Green and colleagues found that somewhere between 0.13 and 0.75 per cent of available carcasses needed to carry a lethal dose to explain the collapse. Fewer than one carcass in every hundred.
That works because of how vultures live. They are long-lived, they breed slowly, usually a single egg, and they are social feeders. Hundreds of birds will come down onto one carcass. So a single treated cow does not kill one vulture. It can kill a crowd of them, drawn from a wide area, all at once. Repeat that a few times a year across a subcontinent and you can take out a species without anybody noticing there is a poison involved.
The job nobody was paying for
India has an enormous livestock population, and for as long as anyone can remember the disposal of dead animals was handled, free and immediately, by birds. A vulture flock can reduce a carcass to bone in about half an hour. Their stomach acid is corrosive enough to destroy anthrax spores, rabies virus and cholera bacteria, so the carcass is not merely eaten, it is sterilised.
Take that away and the carcasses stay. They rot in the open, or get pushed into waterways, or they get eaten by something else. The something else, mostly, was feral dogs and rats, which are exactly the scavengers you do not want doing the job, because unlike vultures they survive what they eat and then walk into villages.
Government figures put India's feral dog population at roughly 17 to 18 million in the early 1980s and close to 30 million by 2005. India already carries the largest rabies burden in the world, with roughly 20,000 deaths a year, around 96 per cent of them from dog bites.
What it cost, and how confident we can be
Two separate attempts have been made to price this, and it is worth keeping them apart.
An earlier estimate attributed roughly 38.5 million additional dog bites and about 47,000 extra rabies deaths to the surge in feral dogs that followed the vultures' disappearance.
The bigger number comes from an economics paper. In October 2024, Eyal Frank and Anant Sudarshan published "The Social Costs of Keystone Species Collapse" in the American Economic Review. They compared human death rates in Indian districts that had been good vulture habitat against districts that had not, before and after the collapse, which lets them isolate the effect of losing the birds from everything else changing in India at the time. They found human mortality rose by more than 4 per cent in the affected districts, which works out at around 100,000 additional deaths a year between 2000 and 2005, close to half a million in total, and roughly 69 billion dollars a year in mortality damages.
That figure deserves a caveat, and the authors would give it themselves. It is a statistical estimate from a model, not a count of named people. Nobody has a list. What the study establishes is that when the vultures went, people in the places that had relied on them started dying at a measurably higher rate, and the most plausible route runs through rotting carcasses, contaminated water and more dogs. The precise number will be argued over. The direction and the scale are hard to dismiss.
The towers that stopped working
One consequence was not about disease at all. Zoroastrian tradition holds earth, fire and water to be sacred and not to be defiled by a corpse, so Parsi funerary practice leaves the dead on open stone towers, the dakhmas, for vultures. In Mumbai this had worked for centuries. The birds would strip a body within roughly half an hour.
Then the vultures stopped coming, and there was no version of the practice that worked without them. Bodies remained for weeks. The community has tried solar concentrators to dry the remains instead, which function after a fashion and not at all through the monsoon, and the argument over what to do has run for years. A veterinary painkiller broke a three thousand year old religious rite, which is not a sentence anyone expected to have to write.
The ban, and the drugs that followed it
India banned veterinary diclofenac in 2006, and Nepal and Pakistan did the same that year. The declines slowed. Research since has confirmed only two anti-inflammatories as safe for vultures at the doses they are likely to meet in the wild: meloxicam and tolfenamic acid.
The trouble is that diclofenac was not the only harmful drug on the shelf, and banning it created a gap that other compounds filled. Since 2008 at least eight wild white-rumped vultures have been found dead in India with visceral gout and significant tissue residues of nimesulide. Veterinary ketoprofen and aceclofenac were banned in July 2023, and aceclofenac mattered particularly because the animal's body converts it into diclofenac. Veterinary nimesulide was finally prohibited by gazette notification in December 2024, with states beginning enforcement through 2025.
So the regulatory fix took about eighteen years from the identification of the cause to the closing of the last major loophole, and enforcement is still uneven.
- Mid 1990sDiclofenac comes off patent. Cheap generics reach Indian markets and it becomes a routine treatment for working cattle.
- 1996Vibhu Prakash finds the nesting count at Keoladeo has halved since 1987. Nobody yet knows why.
- February 2004Oaks and colleagues publish in Nature, tying the kidney failure directly to diclofenac residues.
- 2006India, Nepal and Pakistan ban the veterinary use of diclofenac. The declines slow.
- July 2023Veterinary ketoprofen and aceclofenac banned. Aceclofenac mattered because the animal turns it into diclofenac.
- December 2024Veterinary nimesulide prohibited by gazette notification, closing the last major loophole.
Where it stands now
The conservation response has been substantial. The Jatayu Conservation Breeding Centre at Pinjore in Haryana, set up in 2001 by the Bombay Natural History Society with the Haryana Forest Department, was the first such facility in Asia, and the breeding network has since produced hundreds of birds. Releases into the wild began in 2016. Vulture Safe Zones try to clear toxic drugs from the areas around release sites.
Whether any of this is producing a recovery is where sources part company. Popular accounts often say the populations are slowly recovering. The monitoring data is more cautious. The eighth road transect survey, covering more than 16,000 km of road across 13 states in northern, western and central India in 2022, found population rates hovering around stability. Not falling any more, which after what happened is a real achievement. But not climbing either.
Stable at close to nothing is still close to nothing. The white-rumped vulture, a bird that used to darken the sky over Indian towns, is now counted in the low thousands.
The uncomfortable thing about this story is that nobody did anything wrong in any way that felt wrong at the time. A farmer treated a sick animal with a legal, cheap, effective drug. That is the whole of it. The service the vultures had been quietly running, clearing and sterilising the country's dead livestock at no charge to anyone, had never appeared in any budget, so nothing flagged when it stopped. We found out what it was worth by the only method available once it was gone, which was to pay for it in another currency.
