In the early 1980s, three species of Gyps vulture lived across South Asia. Experts estimated their total population at around 40 million birds. By 2017 the estimate for the same three species was about 19,000.
Hunting did not cause this. Habitat loss did not cause it. Nobody wanted it to happen. The cause was an anti-inflammatory drug. Farmers gave it to cattle so the animals could work through pain. It took years to find this cause. By then, the birds were almost all gone.
Which birds, and how much they fell
Three species suffered most. The first is the white-rumped vulture, Gyps bengalensis. People once thought it was one of the most common large birds of prey on the planet. In India it fell by an estimated 99.9 per cent between 1992 and 2007. From 2001 to 2007, it lost around 48 per cent of its remaining population every year.
The other two are the Indian or long-billed vulture, Gyps indicus, and the slender-billed vulture, Gyps tenuirostris. Each fell by about 97 per cent in the same period, at about 22 per cent a year. The IUCN listed all three as Critically Endangered. It listed the long-billed vulture from 2002.
A 97 per cent fall and a 99.9 per cent fall look similar. But the birds that remain are very different in number: about 3 in every hundred, against 1 in every thousand.
The sick birds at Bharatpur
Vibhu Prakash of the Bombay Natural History Society was the first person to measure the problem. He studied raptors at Keoladeo National Park in Bharatpur. In 1987 and 1988 he counted 353 nesting pairs of vultures in the park's 29 square kilometres. By 1996 that count was about half.
Next to the empty nests, he found something stranger. Vultures sat with drooping necks and no energy, sometimes for weeks. Birds lay dead in the trees and in the nests. Post mortems showed chalky white deposits on the internal organs. This is visceral gout, the sign of kidney failure.
Kidney failure was the cause of death, but what caused the kidney failure? Some experts suspected a pesticide. Others suspected an unknown virus, and for a time this was the main theory. It was a frightening one. Nobody can stop a virus that spreads through the vultures of a whole continent.
The answer came from Pakistan. A team led by the veterinary scientist J. Lindsay Oaks published in Nature in February 2004. The team followed colonies of white-backed vultures and tested the dead birds. The birds that died of renal failure and visceral gout had diclofenac residues in their tissues. The birds that died of other causes did not.
Then the team confirmed it directly. They caused the same kidney damage in vultures that got the drug. They caused it also in vultures that ate meat from livestock treated with diclofenac. Later that year, a separate analysis in the Journal of Applied Ecology showed the same pattern across the subcontinent.
How a cow's painkiller emptied the sky
Diclofenac is a normal non-steroidal anti-inflammatory drug. Its patent ended in the mid-1990s. Cheap generic versions came to Indian markets. It became a routine treatment for working cattle. An animal that is lame or has a fever gets a dose and continues to work. There is nothing evil in this. A farmer takes care of an animal that the farmer depends on.
Most Indians do not eat cattle. So when a cow dies, people put the body outside. For centuries, vultures came to eat it. If the animal got diclofenac shortly before death, the residue stayed in the carcass. A vulture that ate it died of kidney failure within days.
Very little contamination was necessary.
Modelling by Rhys Green and colleagues found that between 0.13 and 0.75 per cent of available carcasses needed to carry a lethal dose to explain the collapse. That is fewer than one carcass in every hundred.
This is possible because of how vultures live. They live long and breed slowly, usually one egg at a time. They also feed in groups. Hundreds of birds can land on one carcass. So one treated cow does not kill one vulture. It can kill a large crowd of them from a wide area, all at the same time. If this happens a few times a year across a subcontinent, a species can disappear. And nobody sees that a poison is the cause.
The free service that stopped
India has a very large livestock population. For as long as anyone can remember, birds removed the dead animals, at no cost and immediately. A vulture flock can strip a carcass to the bone in about half an hour. Their stomach acid is strong enough to destroy anthrax spores, rabies virus and cholera bacteria. So when they eat a carcass, they also sterilise it.
Without vultures, the carcasses stay. They rot in the open, or people push them into rivers, or other animals eat them. Those other animals were mostly feral dogs and rats. These are the worst scavengers for the job. Unlike vultures, they survive what they eat, and then they walk into villages.
Government figures put India's feral dog population at about 17 to 18 million in the early 1980s. By 2005 it was close to 30 million. India already has the largest rabies burden in the world, with about 20,000 deaths a year. Dog bites cause around 96 per cent of them.
The cost, and how sure we can be
Two separate studies tried to calculate the cost. It is important to keep them apart.
An earlier estimate linked about 38.5 million extra dog bites and about 47,000 extra rabies deaths to the increase in feral dogs after the vultures disappeared.
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 two types of Indian districts: districts with good vulture habitat and districts without it. They looked at the years before and after the collapse. This method separates the effect of the lost birds from all the other changes in India at that time.
They found that human mortality rose by more than 4 per cent in the affected districts. That is about 100,000 extra deaths a year between 2000 and 2005, close to half a million in total. The cost in mortality damages is about 69 billion dollars a year.
This figure needs a warning, and the authors would say so too. It is a statistical estimate from a model. It is not a count of named people. Nobody has a list. The study shows one thing clearly. When the vultures disappeared, more people started to die in the places that depended on them. The most likely route is rotting carcasses, dirty water and more dogs. People will argue about the exact number. But it is hard to reject the direction and the scale.
The towers that stopped working
One result had nothing to do with disease. Zoroastrian tradition says that earth, fire and water are sacred, and a corpse must not pollute them. So Parsi funerals leave the dead on open stone towers, the dakhmas, for vultures. In Mumbai this worked for centuries. The birds cleaned a body in about half an hour.
Then the vultures stopped coming. The practice could not work without them. Bodies stayed for weeks. The community tried solar concentrators to dry the remains. These work partly, and they do not work at all in the monsoon. The argument about what to do has continued for years. A veterinary painkiller broke a religious rite three thousand years old.
The ban, and the drugs that came next
India banned veterinary diclofenac in 2006. Nepal and Pakistan did the same that year. The declines slowed. Since then, research has confirmed only two anti-inflammatories as safe for vultures at the doses they will probably meet in the wild: meloxicam and tolfenamic acid.
But diclofenac was not the only dangerous drug for sale. When India banned it, other drugs filled the gap. Since 2008, people have found at least eight wild white-rumped vultures dead in India with visceral gout and significant tissue residues of nimesulide.
India banned veterinary ketoprofen and aceclofenac in July 2023. Aceclofenac was especially important, because the animal's body changes it into diclofenac. A gazette notification finally banned veterinary nimesulide in December 2024. States started to enforce it through 2025.
So the legal fix took about twenty years, from finding the cause to closing the last major loophole. And enforcement is still not equal everywhere.
- Mid 1990sThe diclofenac patent ends. Cheap generics come to Indian markets, and the drug becomes a routine treatment for working cattle.
- 1996Vibhu Prakash finds that the nesting count at Keoladeo is half of the 1987 count. Nobody knows why yet.
- February 2004Oaks and colleagues publish in Nature. They link the kidney failure directly to diclofenac residues.
- 2006India, Nepal and Pakistan ban veterinary diclofenac. The declines slow.
- July 2023India bans veterinary ketoprofen and aceclofenac. Aceclofenac was important because the animal changes it into diclofenac.
- December 2024A gazette notification bans veterinary nimesulide. This closes the last major loophole.
The situation now
The conservation response has been large. The Bombay Natural History Society and the Haryana Forest Department set up the Jatayu Conservation Breeding Centre at Pinjore in Haryana in 2001. It was the first such centre in Asia. Since then, the breeding network has produced hundreds of birds. Releases into the wild started in 2016. Vulture Safe Zones try to remove toxic drugs from the areas around release sites.
Is this work producing a recovery? Here the sources do not agree. Popular articles often say the populations are slowly recovering. The monitoring data is more careful. The eighth road transect survey took place in 2022. It covered more than 16,000 km of road across 13 states in northern, western and central India. It found that population rates were about stable. They are not falling any more, and after this disaster that is a real success. But they are not rising either.
Here, "stable" means stable at a very low level. The white-rumped vulture was once a common sight over Indian towns. Now its numbers are in the low thousands.
The uncomfortable part of this story is that nobody did anything that felt wrong at the time. A farmer treated a sick animal with a legal, cheap and effective drug. The vultures cleaned and sterilised the country's dead livestock for free. This service never appeared in any budget, so no alarm sounded when it stopped. Its value became clear only after it was gone: in dog bites, rabies and human deaths.
