“The villagers were the first to notice the difference,” Vibhu Prakash Mathur recalls. It was the mid-1990s, and Prakash was working at Keoladeo National Park in Rajasthan state, India. “One day they came to me complaining about the rotting carcasses in the fields, and said that the vultures were disappearing from the sky“.

Vultures, an unexpected lynchpin

Vultures aren’t a well-loved species. They are associated with death, and its most macabre side at that. They conjure images of decomposing bodies and rotting flesh. Many see them as revolting, and even those who don’t are unlikely to feel much affection for these large birds.

However, vultures have a vital role within the ecosystems they inhabit. The reason for this is simple: they’re scavengers, or saprophages – beings who consume dead biomass. Like hyenas and jackals, they feed on the carcasses of animals they found already dead. “They are probably the only species on the planet that has evolved for scavenging,” says Prakash, who is now the Deputy Director of the Bombay Natural History Society. Jackals have other sources of food. Vultures don’t.

Throughout their evolutionary journey, this characteristic made vultures extremely efficient scavengers. These birds can locate carcasses from 100 kilometres away and quickly communicate the information to other vultures. This is the purpose of the wide swooping circles they make in the air. These movements are highly visible from the ground as well, notifying other scavenger species of carcasses that they might otherwise not find. Vultures can also ingest large amounts of food: according to Prakash, a vulture can eat its own weight in food in one day. The average across the animal kingdom hovers around 5 per cent.

Thus, carcasses are quickly disposed of. In the absence of vultures, decomposition times for a carcass triple, according to a study published in Conservation Biology. This aspect should not be underestimated: the longer it takes for a carcass to decompose, the higher the likelihood of fungi and bacteria – and therefore illnesses – spreading.

Vultures do such a thorough cleaning job that nobody else can do – quickly, efficiently, without any expense. They simply can’t be substituted.

Vibhu Prakash Mathur

“Vultures often intervene before potentially dangerous spores can form. Once they have consumed their prey, the risk of diseases spreading disappears because neither fungi nor bacteria can survive within vulture’s stomachs. For other scavengers, it doesn’t work like that,” Prakash concludes. “Vultures do such a thorough cleaning job that nobody else can do – quickly, efficiently, without any expense. They simply can’t be substituted“. The importance of their ecological function is reflected in the role vultures have in India’s religious traditions.

Vultures as mythological saviours

In the Hindu epic Ramayana, the vulture god – known as Jatayu – is a saviour. His story is linked to the kidnapping of the goddess Sita, the wife of Rama – a god that some Hindu traditions see as the supreme being. It is told that Sita was kidnapped by the demon Ravana and imprisoned upon Git Bahari, “vulture mountain”. Jatayu tried to save her, but the demon chopped off his wings and he fell to the ground. His sacrifice, however, is still remembered. The rocks in Kerala still bear the holes made by Jatayu’s beak as he drew his last breath.

The Parsi – a small, ancient community that originated in Persia and is now concentrated mainly in Mumbai – believe that vultures are more than just mythological divinities. Since the times of the prophet Zarathustra, Parsis have disposed of their dead in dakhmas, also known as Towers of Silence. Earth, fire, and water are sacred elements, and thus cannot be “contaminated” by cadavers. So the bodies of the dead are placed atop these towers, to be consumed by vultures, who dispose of the body in just an hour. The soul’s journey from the world of the living to the land of the dead happens through the “mystical eye of the vulture”.

Today, in Mumbai’s Towers of Silence, corpses lay abandoned, because the vultures are nowhere to be seen.

Until the 1980s, India was home to at least 40 million vultures. They belonged to five subspecies, three of which – Indian, white-backed, and slender-billed – nest in the endless plains at the foot of the Himalayas, created over millennia by the Ganges, Hindus, and Brahmaputra rivers. In the year 2000, all three species were included in the International Union for Conservation of Nature (IUCN) Red List, marked as critically endangered. In just 20 years, India’s vulture population collapsed by 99 per cent. And, for a long time, no one was able to understand why.

Who killed the vultures? 

Prakash’s discovery

In the mid-1980s, while researching his PhD thesis, Vibhu Prakash was monitoring vulture populations in Keoladeo National Park. When he returned in 1996, the villagers living around the park were the first to warn him that something was wrong: the vultures seemed to have disappeared. Unable to find other explanations, the villagers blamed the Americans, because only the Americans could have done something like this. It was rumoured that they had spread pesticides that could kill vultures.

Prakash’s measurements and observations confirmed the villagers’ impressions. Compared to ten years earlier, the number of vultures nesting in the park was halved. Prakash was the first to raise the alarm. However, the phenomenon remained apparently inexplicable. “We first thought it was the lack of food,” Prakash recalls, but further research showed there was plenty of food available. It wasn’t even a question of habitat loss, because there hadn’t been significant changes.

“Then we seriously started considering pesticides. We had begun to notice that some vultures would sit in a very strange position – they would remain with their necks drooping down. However, we collected the carcasses and tested the tissues for pesticides, but we couldn’t find much”. So it wasn’t even the Americans. Nevertheless, by 2000, not a single vulture was nesting in the park.

At the time, the phenomenon already extended far beyond the borders of Keoladeo National Park. When the first nationwide study was carried out, it showed that India’s entire vulture population had crashed by 95 per cent compared to the 1980s. Around this time, Prakash’s team was able to ascertain that kidney failure was the vultures’ cause of death. The reasons behind this, however, were still uncertain. The BNHS decided to ask the international scientific community for help. With support from the Zoological Society of London (ZSL) and the Royal Society for the Protection of Birds (RSPB), they began to look into the hypothesis that the die-off might be caused by a virus.

Pakistan: a turning point

In 2000, a team of researchers from the Peregrine Fund – a US-based NGO that focuses on the conservation of birds of prey all over the world – was also investigating the vulture die-off. First in India, then in Pakistan, the scientists faced a new challenge.

Early on, in Pakistan, “we saw thousands of vultures, a few dead ones as well. This baffled me,” recounts biologist Munir Virani, Executive Vice President of the Peregrine Fund. “Why were there virtually no vultures in India, while in Pakistan you looked in the sky and there were thousands?”.

After obtaining permits to work in Pakistan, Virani and his team, accompanied by Dr Lindsey Oakes, a microbiologist from Washington State University, set up three investigation and diagnostics teams in the field, based in Lahore and other places across the country.

Near the border with India, five rivers flow toward the Ocean. A series of canals connect the rivers, providing the water needed to irrigate cotton, rice, and wheat fields. The canals are flanked by verdant banks, dotted with Sheesham Rosewood trees, which can reach 25 metres in height.

“Every single tree had a vulture nest,” Virani recounts. “There are 66,000 kilometres of canals. And every single tree is marked with a number. So for us, it was so easy”. Virani assembled a group of student researchers, who went among these trees every day, counting nests, collecting samples, and, sometimes, even dead vultures. “So that’s what we did every single day,” Virani adds. “They were out at the crack of dawn. They were counting birds. They were collecting dead birds. They were recording”.

Over three years, the team collected samples from some 2,000 nests. However, in the meantime, the number of nests fell to less than twenty. “We collected nearly 1,870 dead birds,” says Virani. “Every dead bird we found was in good body condition. That told us something: there’s no lack of food in Pakistan, there are carcasses everywhere”. In 2002, the team realised that the situation was out of control: they were witnessing an extinction. But there was something that caught the researchers’ attention. When they examined the birds’ carcasses, they found that their kidneys were covered in white uric acid crystals. This pointed to Avian Visceral Gout. This meant that, as Prakash’s team had also found, there was something destroying the vultures’ livers. But what was it?

“It had to be cheap because the farmers aren’t very wealthy. It had to be readily available over the counter. It had to be something that was causing kidney failure,” explains Virani. The researchers began to suspect that the cause could be anti-inflammatory medication, which can have similar effects on human beings. So they decided to ask farmers what the animals ate, and what medicines they were being given. “What do you give them if they have pain?”, they asked in a survey.

The answer: “Diclofenac. Boom”.

A lethal drug?

Diclofenac is a common anti-inflammatory medication, whose active ingredient is widespread even in Europe. In India and Pakistan, it was extremely cheap and used for both medicinal and veterinary purposes. Farmers used it to treat livestock suffering from ailments ranging from rheumatoid arthritis to mastitis. Likely introduced for veterinary purposes toward the end of the 1980s, it quickly became extremely popular among Indian farmers, so much so that – according to Prakash – it took over about 80 per cent of the livestock drug market.

Diclofenac was killing vultures. If a vulture fed on the carcass of a cow that had been administered diclofenac in the previous 72 hours, it would die. Its death, however, would not be immediate: kidney failure happened after several days. For this reason, the vultures were found far away from the “poisoned” carcasses. This is why it took so long to find the cause of the die-off. “It was really like finding a needle in a haystack”, says Virani.

It was really like finding a needle in a haystack.

Munir Virani

To prove the validity of their theory, the Peregrine Fund team carried out some experiments. They gave vultures diclofenac orally and through buffalo meat. The vultures died, showing the same symptoms found during the sample collection and analysis in Pakistan. The results of the study were presented in 2003 and subsequently confirmed by experiments carried out by the BNHS in India. The research carried out by Oakes and the Peregrine Fund had, for the first time, documented and proved that a drug was responsible for the disastrous collapse of vulture populations.

In 2006, the Indian government decided to ban diclofenac for veterinary use (the law only came into effect in 2008). Vultures, however, kept dying. Over time, Prakash’s team guessed that farmers had started administering diclofenac intended for human use to their livestock.

“But it’s not just Diclofenac,” explains Prakash. “We found out that there are many drugs that are toxic for vultures“. Their names are likely to sound familiar: ketoprofen, aceclofenac, nimesulide, flunixin. “We are putting pressure on the Government to ban their use, but unfortunately, they also receive strong pressure from farmers […] and from the pharmaceutical industry”.

In 2015, the Indian government set limits for diclofenac use, banning all doses higher than 3 millilitres (ml). The dose for a cow is approximately 15ml. All other drugs that might harm vultures are still in use.

When vultures disappear

The vulture die-off in India has left a great void, with serious consequences for human beings as well. It’s no coincidence that the first people to notice the die-off, in the 1990s, were villagers in rural communities.

According to the latest census carried out by the Indian government, there are over 535 million heads of livestock in India, 302 million of which are cattle. For cultural reasons, their meat is rarely eaten by humans. Eating cow meat isn’t allowed in the Hindu tradition, while Muslims can only eat it if it’s slaughtered according to the halal method. The Hindu (80 per cent) and Muslim (13 per cent) populations combined constitute the vast majority of Indian people. Consequently, cows are farmed to produce dairy and leather, but, once skinned, their carcasses are often left in the field. Until recently, vultures were there to dispose of them quickly.

Since the almost complete disappearance of vultures, the importance of these animals to rural communities has become abundantly clear. Biomass disposal systems in India are lacking, and getting rid of carcasses – be it by burning or burying them – is expensive and time-consuming. It also makes life harder for those who, in rural communities, earn their living by collecting the bones left behind by vultures. These bones are then sold to industrial facilities that grind them into powder and use them to make various chemical products.

The negative outcomes aren’t just economic either. The disappearance of vultures has left an ecological void that is impossible to fill. Without these birds, abandoned putrefying carcasses become a serious health hazard – “especially in countries like India, which is a hot and humid country and […] doesn’t have an organized carcass disposal system,” says Prakash. This has a negative effect on the spread of water-borne diseases, such as cholera. And that’s not the worst of it: without vultures, carcasses become the targets of wild dogs.

These dogs feed on carcasses but, unli