The worst seems to be over for South Asia's vultures, which just a decade ago appeared to be headed straight for extinction.
Hundreds of thousands were dying every year. Scientists had no idea why. Only a last-minute stroke of luck revealed how the majestic creatures were being accidentally poisoned by medicine given to cows.
The medicine was banned in animals in 2006. Its use hasn't ceased completely, but it's diminished enough to slow the vulture die-off. Their survival is far from assured, but at least they have a chance.
"There used to be millions, right in the heart of all the big cities. They'd breed in gardens, in the trees along city streets," said University of Cambridge zoologist Rhys Green. "Those are all gone now. There are no colonies anymore. Will they get back to that? I don't think so, but they could get back to having safe populations."
Green, the lead author of a vulture assessment published May 11 in Public Library of Science One, started working with the birds in 2004. Just months earlier, researchers led by the late Washington State University microbiologist J. Lindsay Oaks had discovered that diclofenac, an anti-inflammatory drug commonly given to livestock, was killing the Indian subcontinent's three species of vulture.
His discovery was a mix of scientific detective work and old-fashioned good luck: Oaks happened to be interested in Middle Eastern falconry, and heard of fatal cases of diclofenac poisoning. On a hunch he decided to test for the drug in India's vultures, populations of which had declined by 95 percent in the preceding decade.
The birds had been dying inexplicably from renal failure and gout, with researchers searching in vain for evidence of heavy metals or pesticides or disease. Side effects from veterinary medicine hadn't even been considered: Until then, they'd never caused a mass wildlife die-off. If Oaks had discovered the drug in the vultures just a couple years later, it would have been too late.
>'Researchers calculated that every vulture had a 1 in 100 chance of dying every time it ate a meal.'
Linking diclofenac to the deaths gave researchers an immediate insight into what Green called a "perfect storm" of circumstances. Until the early 1990s, diclofenac was the intellectual property of pharmaceutical giant Novartis. When its patent expired, India's sophisticated generic drug industry ramped up production, flooding the country with cheap, highly-potent diclofenac. Farmers bought millions of doses. Cattle are sacred in many parts of South Asia, and diclofenac helped ease the pains of elderly beasts of burden.
Because they are sacred, however, the bodies of dead cattle were not eaten or rendered. Instead they were left in fields to be eaten by vultures. In 2004, carcass surveys found one in 10 to be contaminated with diclofenac, and researchers calculated that each vulture had a 1 in 100 chance of dying every time it ate a meal. By 2006, India, Nepal and Pakistan had banned the veterinary use of diclofenac.
In the new paper, Green and colleagues studied the bans' effect, analyzing data from surveys of carcasses collected across India between 2004 and 2008. They found that contamination had dropped from 10.1 percent to 5.6 percent by 2008 -- a sign that the ban is working, though not as fast as they'd hoped. Annual death rates dropped from an astronomical 80 percent before the ban to 18 percent.
"If we can get that down to 5 percent, then there's a chance" that the vultures will survive, said Green. "That's still a decline, but we could counteract it by putting out food for the birds and protecting their nest sites. We could compensate for that level of decline."
There were other encouraging signs in the data. In 2008, the number of carcasses contaminated with meloxicam -- an alternative, vulture-friendly anti-inflammatory -- outnumbered those tainted by diclofenac. This has occurred in spite of the fact that the ban has been unevenly enforced. According to Green, the success represents outreach efforts to veterinarians and farmers, many of whom hold vultures in high esteem.
In Hindu mythology, vultures have a god, Jatayu. Among Parsi communities, for whom religious tradition forbids burial and cremation, corpses have historically been left on platforms for vultures to consume. In the birds' absence, Parsis have turned to other methods of dealing with their dead, including solar accelerators designed to hasten decomposition, though none have proved as efficient or hygienic as vultures. Their highly acidic stomachs are lethal to bacteria, and flocks could strip a body in minutes.
The loss of vultures is also felt among people who collected leftover cattle bones and ground them into fertilizer. Now the corpses of cattle are buried -- as sacred animals, they often can't be eaten -- or dragged away by an exploding population of feral dogs, which have become a reservoir of rabies.
"There's no longer a symbiosis between vultures and people. Now, instead of vultures, there are lots and lots of semi-wild dogs," said Green, who thinks that the dogs' rise to ecological prominence will prevent the vultures from ever recovering their original role. Still, that the vultures could have any sort of future was almost inconceivable a decade ago. Even though 99 percent have died, the remaining one percent may be enough.
"They breed slowly, only rearing a maximum of one chick per year," said Green. "They can increase at a rate of 3 to 5 percent per year. It's never going to be really rapid, but over time it builds up."
Image: A juvenile white-rumped vulture, the hardest-hit of South Asia's three vulture species. For every 1,000 that lived in 1992, just one lives today (Lip Kee/Flickr).
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Citation: "Effectiveness of Action in India to Reduce Exposure of Gyps Vultures to the Toxic Veterinary Drug Diclofenac." By Richard Cuthbert, Mark A. Taggart, Vibhu Prakash, Mohini Saini, Devendra Swarup, Suchitra Upreti, Rafael Mateo, Soumya Sunder Chakraborty, Parag Deori, Rhys E. Green. Public Library of Science One, May 11, 2011.
