Image copyright G.Shorrock/RSPB Image caption The population of oriental white-backed vultures is estimated to have crashed by 99.9% since the late 1990s

After the devastation wrought by a drug on Asian vulture populations, a project hopes to begin releasing captive-bred birds into the wild by 2016.

The Saving Asia's Vultures from Extinction (Save) programme says it plans to release up to 25 birds into a 30,000-sq-km drug-free "safe zone".

Diclofenac - used by vets on cattle - was identified as causing a crash in vulture numbers and banned by India.

But, says Save, the version for human use is still given illegally to cattle.

Diclofenac was banned for use by vets and farmers in 2006 because of its effect on vultures that feed on livestock carcasses.

The link between the anti-inflammatory drug, used to reduce swelling in injured or diseased animals, and the devastating demise of Asia's vulture populations was firmly established in 2004.

Image copyright C.Bowden/RSPB Image caption Until the breeding programme, the threatened species of vulture had not been bred in captivity

Tests on captive vultures fed carcass flesh traced with the drug produced symptoms that were strikingly similar to those witnessed in sick birds in the wild.

Experts said vultures feeding on cattle either died from acute kidney failure within a few days or lost their ability to reproduce.

Rinkita Gurav from the Bombay Natural History Society - a member of the international Save consortium - said that it was vital to "remove diclofenac from the market completely".

"The veterinary version of the drug was banned in India back in 2006 but the major problem is that the human forms of the drug are being given illegally to cattle," she told BBC News.

"Because of this, it is not completely out of the system... [and] is readily available in pharmacies and chemists."

Environmentally essential

The demise of three species of vulture in South Asia has been directly link to the presence of diclofenac in the environment. These are the oriental white-backed vulture (Gyps bengalensis), long-billed vulture (Gyps indicus) and the slender-billed vulture (Gyps tenuirostris).

Two other species - the red-headed vulture (Sarcogyps calvushave) and the Egyptian vulture (Neophron percnopterus) - also recorded declines in their populations. However, the link between these species' demise and the drug is not as clear as it is with the other three kinds of vulture.

In order to ensure that the species affected do not disappear completely from the wild, Save identified a number of priorities.

One of these was to establish a number of vast "safe zones" for the captive-bred birds to be released within.

The areas have a radius of 100km (62 miles), and the consortium has identified six such areas - some of which cross national borders into Nepal, Pakistan and Bangladesh.

Ms Gurav said the consortium carried out a lot of advocacy work at grassroots levels within these areas in order to remove diclofenac from the environment.

"This work is basically spreading awareness and we have workshops and educational programmes," she explained.

She added that there was a growing awareness of the important role vultures play in the wild.

Image copyright R.Cuthbert/RSPB Image caption Conservationists say the vultures perform a vital environmental service

"They clean a carcass completely so the bacteria or diseases cannot go into the soil or water and contaminate it," she explained.

"There are a lot of farmers that say that they used to see a lot of vultures but now there are very few. Now, they do understand that these birds are very important."

Another key priority identified by Save was the establishment of a captive-breeding programme, which would provide the birds to be released back into the wider environment, once it was safe to do so.

Since 2004, a number of vulture breeding centres have been set up in Nepal and Pakistan, as well as in India.

Funding fears

Chris Bowden, RSPB international species recovery officer and Save programme manager, assessed the centres' progress after a decade of work.

"Bearing in mind that these birds do not breed too well compared with other species - for example, they only lay one egg a year and the other natural constraints we have as a starting point - I think it is going very well," he said.

"Dare I say it, but this year we are likely to break the 100 figure for the number of fledglings produced via the captive-breeding programme.

"We've bred all three species and these species had never been bred before so I think we can be very pleased about the way it is going."

But he acknowledged that a project on this scale was an expensive affair, and costs were set to continue rising.

Mr Bowden observed that if the necessary funding was not in place then it was possible that the programme "may have to take its foot off the gas".

"I am optimistic that we can really get vultures back to the level where they are performing the environmental function that the populations used to perform within my lifetime," he told BBC News. "A few years ago, I would not have said that. But it is not going to be easy; there is still a lot to do."