A common painkiller used to treat both humans and livestock has been implicated in the catastrophic decline of wild vultures in Pakistan. But not everybody is convinced that the real culprit has been found.
Since the 1990s South Asia has witnessed a decline in the population of vultures. Once a highly abundant bird, today the Oriental white-backed vulture (Gyps bengalensis) is listed as critically endangered by BirdLife International. Vultures play an important function in the food chain by acting as scavengers, and there has been a giant ongoing effort to identify the causes for this rapid decline.
Now, a team of 14 U.S. and Pakistani scientists has identified the widely used painkiller diclofenac--a nonsteroidal antiinflammatory drug--as the cause of vulture decline in the Punjab province of Pakistan. They report that the drug causes renal failure and visceral gout in the birds. Even minute dose are toxic to the birds, the team reports online 28 January in Nature. Thirteen of 20 captive vultures fed meat laced with diclofenac died. The team found no evidence of viruses or other toxins that could have crashed the population. "This discovery is significant in that it is the first known case of a pharmaceutical causing major ecological damage over a huge geographic area," says lead author J. Lindsay Oaks, a veterinary microbiologist at Washington State University, Pullman. He adds that the most probable source of diclofenac is the consumption of treated livestock.
However, other experts are not convinced that diclofenac is the only culprit. Vibhu Prakash, an ornithologist and chief of the Vulture Care Center in Pinjore, Haryana, India, says that the drug is rapidly excreted by livestock and is thus unlikely to be responsible for large numbers of bird deaths. Prakash suspects that some as-yet-unknown virus is killing vultures in the subcontinent.
"It is a questionable finding," concurs Mahendra Pal Yadav, a veterinary microbiologist and director of the Indian Veterinary Research Institute in Izatnagar. "Oaks and his team are reading more than the science is offering them." Yadav points out that diclofenac is not widely used in India, which also experienced a large vulture die-off. That suggests there's some other culprit. But Oaks insists that his team's findings are valid, at least for Pakistan. "The data unequivocally show that diclofenac is responsible for the vulture population decline in Pakistan," he says.