By Roland Pease
BBC science correspondent
Wildlife experts are urging the Indian government to ban a widely used veterinary drug in order to save vultures from extinction.
The new drug could offer a lifeline to vultures (Image: RSPB Images)
Numbers have plummeted in recent years because they are being poisoned by traces of the anti-inflammatory drug, diclofenac, in animal carcasses.
A study published by the Public Library of Science says an alternative drug, meloxicam, is harmless to vultures.
Protecting vultures could help prevent the spread of diseases such as rabies.
Meloxicam was first tested on the African white-backed vulture, Gyps africanus, a relative of South Asian species which is not endangered.
Low-dose tests revealed a complete lack of effect on the birds' metabolism, and even experiments with the maximum likely dose produced no harm.
Only at this point were the researchers prepared to try the drug on a handful of Indian vultures.
Three species have seen dramatic declines: the oriental white-backed vulture (Gyps bengalensis), the long-billed vulture (Gyps indicus) and the slender-billed vulture (Gyps tenuirostris).
According to Deborah Pain of the British-based Royal Society for the Protection of Birds (RSPB), who took part in the study, meloxicam is "at least as good as diclofenac as a veterinary drug, if not better."
Dr Pain was speaking to the BBC from Dehli, where animal-welfare groups are hoping to persuade the Indian government to ban diclofenac.
"The government really needs to create an incentive for manufacturers to increase production," she told the BBC.
Oriental white-backed vultures are critically endangered (Image: RSPB Images/Guy Shorrock)
Meloxicam currently costs twice as much as diclofenac, but that could change if production was stepped up.
Indian prime minister Manmohan Singh said last March that diclofenac would be phased out within six months, but little has happened since, according to activists.
They are hoping that at a meeting on Tuesday, organised by the Indian government, they can win a renewed commitment - though the signs, they say, are not encouraging.
Saving vultures from extinction on the subcontinent is not just a matter of pious aesthetics, the experts argue. As vulture numbers decline, so stray dogs are becoming much more numerous, feeding off the increasing number of unattended animal carcasses.
The danger is that they will spread deadly disease, in particular rabies, which is rife in India.
The RSPB, London Zoo and the UK government's Darwin Initiative have also embarked on a programme of captive breeding, which, it is hoped, could be used to re-stock the wild vulture population once conditions are right.