Has Mysterious Killer of India's Vultures Been Found?

John Roach
for National Geographic News
Updated May 4, 2004
When Lindsay Oaks went to Pakistan in the year 2000, there were so many
vultures that he got bored looking at them. Now, three years later, the
raptors are nearly gone. Within a few years, they may be extinct. The
culprit appears to be a drug akin to aspirin and ibuprofen.

In a study that sheds light on a decade-old mystery, Oaks, a veterinary microbiologist at Washington State University in Pullman, and colleagues link the vulture deaths to the recent and widespread use of diclofenac, a non-steroidal anti-inflammatory drug that has become a popular treatment for ailing livestock throughout the Indian subcontinent.

Vultures, which once clouded the skies, were the subcontinent's carcass disposal system. When an animal dies, hide collectors remove the skin, leaving the rest for the birds.

But over the last decade, populations of the Oriental white-backed vulture (Gyps bengalensis), long-billed vulture (Gyps indicus), and slender-billed vulture (Gyps tenuirostris) have declined by more than 95 percent in Pakistan, India, and Nepal. Now, the carcasses rot for days, raising quite a stink throughout the region.

"Any time you have an animal die of disease and its carcass sits around, it's a problem," said Oaks. For example, in India, the rotting carrion supports booming populations of feral dogs, which in turn spread rabies.

Additionally, vultures play an integral part of the Parsi "sky burial" ceremony in which human corpses are left out to be consumed by the raptors. The lack of vultures in places like Mumbai (known earlier as Bombay) is causing significant problems for this ancient tradition, said Oaks.

Mystery Solved?

Until now, the cause of the vulture die-off has been a mystery. Theories ranged from the emergence of an unknown infectious disease to the buildup of pesticides in the vultures' tissues.

Based on an intense, three-year study of three rapidly declining Oriental white-backed vulture colonies in Pakistan, Oaks and his colleagues conclude that the vultures die after scavenging carcasses of livestock with diclofenac residues.

According to the study, which was posted today on the Web site of the science journal Nature, 85 percent of the 259 vultures tested died from visceral gout, a condition in which pasty, chalky white deposits of uric acid coat the internal organs. It is caused by kidney—or renal—failure.

In healthy birds, uric acid is excreted by the kidneys and is seen as the white material in their droppings. When the kidneys fail, uric acid builds up in the bloodstream and crystallizes on organs, especially the heart, liver, and kidneys.

The researchers performed tests to see if viral or bacterial infectious disease, pesticides, poison, heavy metals, or nutritional deficiency could explain the renal failure observed in dead vultures but found no such evidence. Instead, they found a correlation between kidney failure and diclofenac.

"We are pretty much convinced where birds are dying of visceral gout or renal failure it is caused by diclofenac," said co-author Rick Watson, international programs director for The Peregrine Fund in Boise, Idaho, which led the international study team.

Ian Newton, an ornithologist with the Centre for Ecology and Hydrology at the Natural Environment Research Council in Cambridgeshire, United Kingdom, said the study is carefully done and clearly shows the link between diclofenac and the vulture deaths.

"Throughout the region, the timing of vulture decline coincides with the period of diclofenac use, and such massive population declines have not been recorded in related vultures in other parts of the world where the drug is mainly restricted for human use," he said.

Diclofenac Consequences

Oaks and colleagues are currently partnering with the World Wildlife Fund–Pakistan to figure out the economic reasons for why diclofenac has suddenly become widespread throughout the Indian subcontinent, but suspect its growth stems from it being a safe, effective, and cheap pain reliever for animals.

"From a vet's perspective, it is actually a very good drug and there is very little disincentive…to use it," said Oaks. "No one thought it would have these ecological impacts."

Like ibuprofen and aspirin, diclofenac can be used to treat ailments such as a sore leg. Although it cannot cure the leg, the drug can alleviate pain enough to allow an ailing buffalo to ferry a load back to the farm from town, said Oaks.

The unintended consequence comes when livestock die shortly after being treated with the drug. Their bodies contain sufficient residues to cause visceral gout in the vultures.

In order to prevent the extinction of these vultures, Oaks and his colleagues are calling for an immediate ban on the veterinary use of the drug. "We know for a fact that diclofenac is really bad, so the first priority is to get that controlled," said Oaks.

Currently, the use of diclofenac to treat livestock appears to be largely restricted to countries in southern Asia. The vulture crisis research community is concerned, however, that if the drug were used in a similar way in Africa, the Middle East, or Europe, it might affect closely related species in these regions too.

Call for Action

To expedite the transfer of this finding to the appropriate authorities, the researchers have organized an international summit next month in Kathmandu, Nepal. "What the outcome will be we can't tell at this stage, but we will provide every bit of opportunity for the governments to respond appropriately," said Watson.

According to Watson, chief among the appropriate responses is an outright ban on the veterinary use of diclofenac. Other options include an aggressive captive breeding program and actively feeding uncontaminated food to the vultures.

"With such an apparently lethal chemical, the most effective solution would be to ban its use altogether in free-ranging livestock, and in my view it is unlikely that vultures could survive where this chemical is in widespread use," said Newton.

While there are several alternatives to diclofenac, the researchers do not know if any of them are safe for the vultures. Further studies may reveal an answer. In the meantime, they recommend a captive breeding program to ensure viable populations for future re-introduction programs.

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