With a seven-foot wingspan, the oriental white-backed vulture (Gyps bengalensis) was an awesome presence in south Asia until the mid-1990s, when populations in the tens of millions began to collapse. A University of Michigan study led by Jeff Johnson determined the decline was caused by an anti-inflammatory drug, diclofenac, used to alleviate arthritis-like symptoms in livestock. The drug is fatally toxic to vultures.

Although India, Nepal and Pakistan outlawed its manufacture in 2006, diclofenac is still available and birds are still dying.

The scientists said the absence of vultures poses a threat to public health, since uneaten livestock carcasses provide breeding grounds for bacteria.

"We know the problem, and we know the solution," said Johnson, now an assistant professor at the University of North Texas-Denton. "We just need to get diclofenac out of the environment and more birds into protection before it is too late."

The research that included Martin Gilbert, Munir Virani, Muhammad Asim and former University of Michigan professor David Mindell appeared in the Aug. 15 online edition of the journal Biological Conservation.