By Mark Kinver
Science and nature reporter, BBC News
Fewer than 11,000 white-backed vultures could remain in India
Asian vultures could be extinct in the wild within 10 years unless a livestock drug blamed for their rapid demise is eliminated, scientists warn.
A survey showed that the population of the oriental white-backed vulture had crashed by 99.9% since 1992.
India has banned the manufacture of diclofenac, an anti-inflammatory drug for cattle, but it is still on sale to the nation's farmers, the team says.
The findings appear in the Journal of the Bombay Natural History Society.
The researchers also found that the populations of long-billed vulture and slender-billed vulture had fallen by about 97% over the same period.
"Year on year, these two species are declining by about 16%," explained co-author Andrew Cunningham, from the Zoological Society of London (ZSL).
"This is pretty horrific but when you think that the white-backed vulture is declining by about 45-50% each year, that is truly staggering."
The team of Indian and British researchers say the unprecedented demise is a result of the birds being poisoned by traces of the anti-inflammatory drug, diclofenac, in animal carcasses.
Although India's government banned the manufacture of the drug in 2006, Dr Cunningham said the measure has had little impact.
"They have only banned its manufacture for veterinary treatments," he explained, "the manufacture for medical treatments are unaffected by this ban.
"The treatment of animals with diclofenac also hasn't been banned, so people are now just using the medical version to treat animals rather than buying the veterinary one."
It also appears as if the drug is still being imported from producers in other countries, which means fresh supplies are making their way onto the market.
A few years ago, researchers identified an alternative drug called meloxicam that was not toxic to vultures.
But the take-up of meloxicam was inhibited because it was about twice the price of diclofenac.
However, as more companies began to produce the vulture-safe alternative, the price fell.
"The price difference is not as much as a problem as it appeared to be two or three years ago," observed Dr Cunningham.
"It appears to be a painfully slow process, and far too slow to be sure that the vultures are going to survive."
In order to ensure there is viable population of the threatened species, conservationists have set up a number of captive breeding centres.
The Indian network, underpinned by the UK government's Darwin Initiative, is being led by Bombay Natural History Society (BNHS), with support from overseas organisations, including the RSPB and ZSL.
Captive breeding may be the only hope for a number of species
One of the centres recently enjoyed its first success when two oriental white-backed vulture chicks were born.
"They look as if they are doing well," Dr Cunningham told BBC News.
"It is quite heart-warming to have a bit of light at the end of the tunnel, but it is going to be a long, long haul over the next 15-20 years before we get anywhere near to being able to release any birds.
"These birds are difficult to catch in the wild now because there are so few of them, so it is easier to find where they are nesting and get them as youngsters.
"But they are not sexually mature until they are about five years of age, and successful breeding normally takes two or three seasons."
The ZSL researcher is also concerned that the problems facing vultures in India could occur elsewhere in the world.
"We are particularly worried about Africa because diclofenac has recently started to be marketed as a veterinary drug.
"There are vultures there that are very closely related to the Indian vultures, so we know that they are susceptible.
Dr Cunningham added that the drug was also being used in South America, but the vulture species there were evolutionarily distinct from old world vultures and not affected.
"I don't think we should take our eye off the ball as far as getting this drug out of the ecosystem is concerned."