They swoop down in flocks and can consume an entire dead cow in a matter of minutes.
It's no wonder vultures don't always have the best reputation.
But in India, Pakistan and Nepal, the important role of these scavengers has been underlined as the birds are near extinction. Their rapid decline has been blamed on a veterinary drug, diclofenac, which the vultures ingest when feeding off treated cattle carcasses. New research shows the widely used anti-inflammatory drug is highly toxic to an entire family of vultures and may cause the birds' demise around the globe.
Debbie Pain, a research scientist at the Royal Society for the Protection of Birds in England, said the situation was "extremely urgent."
"Populations of three vulture species affected by diclofenac in South Asia have declined by more than 97 percent since the early 1990s," Pain said.
Left to Rot
What's to miss about some flesh-eating scavengers? Pain explained that the birds played a critical role in human and environmental health. For example, when cows die in India and Pakistan, it is custom to leave the carcasses where they are. In India, this is partly due to religious Hindu reasons because the cow is considered sacred.
Normally flocks of vultures -- there are three main varieties in the region -- then quickly devour the carcasses and reduce them to a tidy pile of bones. But today, with populations nearly extinct, the dead animals often rot. The deteriorating flesh attracts wild animals, such as feral dogs, cats and rats, which then flourish and pose a risk for attack on people.
The rotting carcasses also become breeding grounds for diseases such as anthrax.
"If a carcass is unconsumed for a day, anthrax within the animal has a chance to form spores, and these spores are incredibly resistant," said Rick Watson of the Peregrine Fund in Boise, Idaho. "That's how the disease spreads. So you set yourself up for increased incidence of disease -- both animal and human."
Diclofenac is not poisonous to humans -- in fact, it has been used in human medicine for nearly 40 years. But as the expression, "canary in the coal mine" suggests, birds -- in this case, vultures -- are much more sensitive. So when the patent on the drug expired and the drug became cheaper to buy, veterinarians began administering it widely to cattle in 1993 in India and in Pakistan in 1998.
"It's like a cure-all for veterinarians," Watson said. "It's like the doctor telling us to take two aspirin."
There were immediate consequences.
"It causes kidney failure in the vultures," Watson explained. "The kidneys shut down so the uric acid precipitates inside and on the surface of internal body organs. It destroys the animal inside and out within 24 to 72 hours."
Poisonings Could Spread
So far, three species of vultures have been severely affected -- the long-billed vulture, the slender-billed vulture and the oriental white-backed vulture. Pain's new research, appearing in the journal Biology Letters, shows that the drug is just as lethal to other related vulture species. There is little concern the problem will spread to the United States, because the drug is not approved for use in cattle here and ranchers generally don't leave carcasses to rot in the field.
"Sometimes birds are poisoned by other drugs used in cattle," said J. Lindsay Oaks of the department of veterinary microbiology and pathology at Washington State University. "But it's a sporadic problem, not a population threat."
But the problem could extend to vultures in Africa where carcasses are sometimes left to rot in large patches of wilderness.
Watson's and Pain's groups have tried persuading local governments to ban the drug, but their efforts and government efforts haven't had much effect so far. The vulture populations have gotten so low that Pain has argued the only way to save the scavengers from extinction is to begin holding them in protective captivity.
"I wish there is something we could do to curb the use of the drug," Watson said. "We're right on the edge, but we're at a loss over what to do."