New research, published in the Journal of Applied Ecology, shows that exposure of vulture populations to a surprisingly small proportion of livestock carcasses contaminated with the drug - less than 1% - is sufficient to cause the rapid declines in vulture populations observed in India, Pakistan and Nepal over the past ten years. The study also found that the proportion of dead vultures with symptoms of diclofenac poisoning is close to that expected if this was the sole cause of the declines.
Dr Rhys Green of the Royal Society for the Protection of Birds and the University of Cambridge, the lead author of the new paper, said: "Our study indicates that diclofenac poisoning is the main cause - possibly the only cause - of these vulture declines, which are among the most rapid ever recorded for any wild bird. Time is running out if we are to save these species. Governments, drug companies, vets, livestock owners and conservationists should act together now to solve this problem."
The research builds upon a study by Lindsay Oaks and colleagues of The Peregrine Fund, published in Nature in January 2004, which showed that tissues of livestock treated with the standard veterinary dose of diclofenac shortly before death were lethal to captive vultures and that a high proportion of wild vultures found dead in Pakistan were contaminated with diclofenac and had the same symptoms as the poisoned birds in their experiments.
The most recent population surveys in India, carried out by the Bombay Natural History Society in 2003, show that the population of the oriental white-backed vulture (Gyps bengalensis) has fallen by more than 99% since the early 1990s, with that of the long-billed vulture (Gyps indicus) having fallen by more than 97%. These declines are continuing: white-backed vulture populations declined by an average of 50% in each year between 2000 and 2003 in both India and Pakistan and long-billed vultures in India declined by 22% per year during the same period. The rare slender-billed vulture (Gyps tenuirostris) is also declining rapidly. All three species have been listed as Critically Endangered, the highest level of extinction risk, by IUCN - The World Conservation Union.
Diclofenac is widely used and distributed for livestock treatment in India and Pakistan, so it will probably take a considerable time to remove it from the vultures' food supply. According to Dr Asad Rahmani, Director of the Bombay Natural History Society: "It will be difficult to remove diclofenac from the environment until drugs that are safe for vultures have been identified, so we urgently need captive breeding of vultures as a precaution until that has been achieved".
Journal
Journal of Applied Ecology