A CONSERVATION catastrophe has become a human tragedy. The mass poisoning that has killed millions of India's vultures may have indirectly claimed the lives of almost 50,000 people, according to an analysis of the wider impacts of the bird die-off.
Since the 1990s, numbers of long-billed, slender-billed and oriental white-backed vultures have declined at an unprecedented rate. All three species could be driven toward extinction within a decade. The cause is a veterinary drug called diclofenac, which was routinely given to cattle. When the cattle died, vultures that fed on their carcasses were poisoned by the drug. Although now banned in India, diclofenac is still used to some extent.
It seems the drug has also had an unforeseen knock-on impact. As vulture numbers crashed, the population of feral dogs across India surged, feasting upon cattle carcasses that would otherwise have been stripped bare by birds.
The catastrophic decline of griffon vultures in south Asia is being caused not by a mysterious disease, as had been thought, but a common painkiller given to sick cattle.
If the treated animal dies and is eaten by vultures, a single meal can be enough to kill the bird. The scientists who made the discovery now want the drug banned from veterinary use and are holding a meeting next week with officials from Nepal, India and Pakistan.
Griffon vultures are huge scavengers and used to be ubiquitous in south Asia. But their population has declined drastically since the mid-1990s, and one species is near extinction.
As a result, animal carcasses rot outside villages, attracting rabies-ridden packs of dogs. The Parsee religious community in India is also in crisis, as it disposes of its dead by feeding them to vultures.
Lindsay Oaks, a veterinary microbiologist at Washington State University in Pullman, and colleagues looked for pathogens or toxins in freshly dead vultures from breeding colonies in Pakistan and Nepal by sending tissues back to US laboratories for analysis.
Efforts by Andrew Cunningham of the Zoological Society of London, UK, and colleagues to establish the cause of the vultures' decline in India were hindered by that county's laws banning the export of genetic material.
Vultures that have died in the decline have kidney damage and uric acid crystals throughout their bodies, but Oaks's group could find no disease germs or environmental toxins. Vultures that died following pesticide poisoning or collisions had no uric acid.
"We started wondering if they could be exposed to any veterinary drugs in the dead livestock they eat," says Oaks. They discovered that diclofenac, which can cause kidney damage, is very heavily prescribed by local vets, and its use increased over the same time period as the vulture decline. The cheap drug is used to treat lameness and injury - common conditions before a buffalo or cow dies.
Analysis of the kidneys of dead vultures with uric acid symptoms revealed diclofenac residues, while no residues were found in other birds.
The researchers also gave diclofenac, and meat from animals treated with diclofenac, to 20 non-releasable vultures rescued from nesting colonies. "We hated to do it," says Oaks. The diclofenac killed these vultures in very small doses, with the same symptoms as the dead, wild vultures. Furthermore, the higher the dose of the drug, the more likely the vultures were to die.
Vultures come from miles around to feed on a carcass, so each gets a small bit of many animals. Rhys Green of the UK's Royal Society of the Protection for Birds calculates that only one in 250 dead cattle needs to have been recently treated with diclofenac to cause a decline in vultures of 30 per cent per year - about what has been observed.
Cunningham is now trying to find out whether diclofenac is also responsible for the decline in India. "This may be a breakthrough", he told New Scientist. "We hope so, as this would greatly improve the chances for an eventual recovery of the species."