As if it weren't bad enough that 99.9 percent of Asian vultures have been killed off in the past 20 years, now comes news that yet another potential man-made disaster waits in the wings.

Millions of Asian vultures, particularly those in India, have died off over the last two decades after being poisoned by the veterinary drug diclofenac. The vultures eat dead cattle and other livestock treated with the drug, then go into renal failure.

Now scientists have discovered that another veterinary drug, ketoprofen, is also fatal to the birds. Vultures which feed on the carcasses of livestock recently treated with ketoprofen suffer acute kidney failure and die within days of exposure.

The research was published this week in the journal Biology Letters.

Ketoprofen, like diclofenac, is an anti-inflammatory drug administered to livestock to reduce pain and swelling caused by rheumatism or arthritis. It is sold under a variety of brand names.

The conservation organization BirdLife International, which sponsored the new research, is now calling for tighter controls on ketoprofen. The group is also calling for greater use of another drug, meloxicam, which is no longer under patent and is not fatal to vultures.

"Only meloxicam has been established as a safe alternative for vultures, while at the same time being an effective drug for treating cattle," Vibhu Prakash, director of the Vulture Program of the Bombay Natural History Society, said in a prepared statement. "We would like to see other safe alternatives, but it should be the responsibility of the Indian pharmaceutical industry to test these to determine their safety to vultures."

Image: The Indian white-rumped vulture (Gyps bengalensis), a critically endangered species which has lost 99.9 percent of its population due to diclofenac poisoning