Yet another hypothesis to explain decline in vulture population

Another theory has implicated a commonly used veterinary medicine for the large-scale disappearance of vultures from the Indian sub-continent. The theory proposed by Lindsay Oaks of the Washington State University, usa, however, raises more questions than it answers. Ornithologists estimate that more than one lakh vultures have disappeared in India since 1997. A similar trend has been reported in Pakistan during the last three to four years. Out of the eight species of vultures found in the sub-continent, two are on the brink of extinction -- about 90 per cent of the white-backed vulture (Pseudogyps bengalensis) and the long-billed griffons (Gyp fulvus) have vanished till now

 
By T V Jayan
Last Updated: Saturday 04 July 2015

Are vultures dying because the (Credit: Pradip Saha / CSE)another theory has implicated a commonly used veterinary medicine for the large-scale disappearance of vultures from the Indian sub-continent. The theory proposed by Lindsay Oaks of the Washington State University, usa, however, raises more questions than it answers. Ornithologists estimate that more than one lakh vultures have disappeared in India since 1997. A similar trend has been reported in Pakistan during the last three to four years. Out of the eight species of vultures found in the sub-continent, two are on the brink of extinction -- about 90 per cent of the white-backed vulture (Pseudogyps bengalensis) and the long-billed griffons (Gyp fulvus) have vanished till now. Three others in the genus of Gyps are affected equally.

Presenting a paper at the recently concluded world conference on the birds of prey at Hungary on May 20, 2003, Oaks postulated that diclofenac, a drug used to treat sick cattle and buffaloes, is highly toxic to the white-backed vultures -- the predominant variety in India and Pakistan. Diclofenac is also prescribed as a painkiller and anti-inflammatory drug for humans.

Till now, scientists examining the massive vulture decline have hypothesised many reasons for the unnatural happening, including human persecution, infectious diseases, unbridled pesticide usage and lack of food (due to the unavailability of animal carcasses in urban and rural areas as a result of cleanliness drives launched by municipalities and corporations).

Oaks, who has been studying the intriguing phenomenon in Pakistan with support from the us-based Peregrine Fund, could not find a disease-causing pathogen in the dead vultures. Similarly, tests for pesticides, metals and other poisonous substances also turned out to be negative. His subsequent enquiries revealed that local cattle and buffaloes, on whose carcasses vultures love to feed, are treated with many medicines, including diclofenac. Oaks tested tissues of 23 vultures that had died due to gout disease - a distinctive condition in which pasty or chalky deposits of uric acid coat the internal organs of the birds. He found that all the tissue samples contained diclofenac. During another experiment, healthy vultures also died when they were fed on the contaminated tissues. Diclofenac also proved to be fatal for three vultures directly given the drug in small amounts.

Commenting on Oaks's findings, Vibhu Prakash, who heads the Bombay Natural History Society's Vulture Care Centre at Pinjore in Haryana, says: "It is certainly a plausible reason as diclofenac is a widely used medicine." Prakash, whose work in the late 1990s brought the Asian vulture crisis into focus, says nobody has so far looked at the problem "from this angle". But he asserts that detailed studies are required before the hypothesis is accepted.

Even scientists at the Izatnagar-based Indian Veterinary Research Institute (ivri) feel the theory could be far-fetched. They assert that diclofenac has been in use for the past three to four years only, whereas the crisis came to the fore around six years ago. However, they admit that the drug can damage the liver on prolonged use.

V S Vijayan, director of the Coimbatore-based Salim Ali Centre for Ornithology (sacon) is also doubtful. He says there is not enough background information available to support the hypothesis. "Moreover, even if we consider it as the reason, it may not be able to account for all the vulture deaths. How many cattle in the country are being treated with diclofenac? It might be happening in organised cattle farming. Nobody administers the drug to stray cattle, which form the majority of livestock in the country," he asserts.

According to Vijayan, the main problems are the unavailability of carcasses, and the spraying of toxic chemicals (disinfectants) on a few that can be found. As regards to the theory of infectious diseases, scientists have so far failed to isolate any disease-causing pathogens. They are even divided over considering the head drooping behaviour of vultures as a symptom of imminent death, with a section arguing that it is a normal resting posture of the white-backed vultures and the long-billed griffons. Even as the cause of their deaths continues to puzzle scientists, these far-wandering birds seem to be spreading the mysterious affliction farther west. Very soon all the Gyps species may be affected worldwide.

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