More evidence has emerged that a drug used to treat livestock is the mysterious killer of vultures on the Indian subcontinent. But some scientists say more proof is needed, and time is running out to save three species from extinction.
The situation is dire: Populations of the Oriental white-backed vulture and long-billed vulture have declined by more than 95% in India since the early 1990s, with similarly drastic declines of the white-backed vultures in Pakistan and of the rarer slender-billed vulture. A study published in January cast suspicion on diclofenac--an anti-inflammatory painkiller used to treat livestock. The drug caused visceral gout and death in captive vultures and was responsible for the deaths of 85% of wild white-backed vultures sampled in Pakistan (ScienceNOW, 28 January). Postmortems of wild vultures in India and Nepal, published online in Biology Letters in July, also found a high proportion with gout and diclofenac residues.
Even so, questions remained about whether diclofenac was the sole culprit, particularly in India, where some researchers doubted the drug was widely used. In the new study, published in the October issue of the Journal of Applied Ecology, conservation biologist Rhys Green of the Royal Society for the Protection of Birds in Bedfordshire, U.K., and colleagues calculate that less than 1% of ungulate carcasses would have to contain a dose of diclofenac lethal to vultures to account for the observed rates of decline in India and Pakistan. Computer models of vulture populations back their conclusion that diclofenac poisoning appears to be "at least the major cause, and possibly the only cause" of the vultures' decline across the Indian subcontinent.
The case on the ground is still circumstantial. Although recent surveys have found some carcasses containing enough diclofenac to kill a vulture, the data are still coming in. Even so, Green and colleagues are calling on vets, pharmaceutical companies, and governments to stop using diclofenac on livestock and help in the hunt for a safe alternative.
The evidence that diclofenac is an environmental hazard is strong enough to warrant curtailing or eliminating its use, wildlife veterinarians Joshua Dein of the National Wildlife Health Center in Madison, Wisconsin, and P. K. Malik of the Wildlife Institute of India told ScienceNOW. But they caution that it's too early to stop the search for other factors that might be contributing to the vultures' decline.
, with additional reporting by Pallava Bagla