What's eating the vulture?

There were 2,000 vultures in Bharatpur's Keoladeo National Park during the 1980s. In 1998 experts could spot only four . Ornithologist Asad Rahmani fears that the vulture is disappearing throughout India. To find out the reason for this decline, the Centre for Science and Environment sent its toxicologist Amit Nair to collect carcass samples -- food for the vulture -- from the park. They had high levels of chemical pesticides. Like vultures, humans are also at the end of the food chain. The pesticide threat is very real to humans as well. Down To Earth analyses

 
Last Updated: Sunday 07 June 2015

What's eating the vulture?

-- Flight into obllivion
The vulture is disappearing in India. Nobody knows why. Some experts blame pesticides

O n october 3, 1998, the Centre For Science and Environment ( cse ), New Delhi, received a letter from Asad R Rahmani, director, Bombay Natural History Society ( bnhs ), Mumbai, mentioning a drastic decline in the vulture population of the Keoladeo National Park in Bharatpur. Rahmani wrote how, within a short span, the number of vultures in the region dropped from 2,000 to just four. He cited observations of his colleague Vibhu Prakash, senior scientist at bnhs 's research station in Bharatpur, who says in the 1980s it was natural to find as many as 350 vulture nests in Bharatpur. But in 1998, Prakash found only four. Sudden declines in bird population is not new for Bharatpur. Between 1987 and 1990, says a bnhs report, some 18 sarus cranes and over 50 ring doves were found dead in the region. More birds dying within the park premises is also a strong possibility. cse sent its environmental toxicologist Amit Nair to Bharatpur to collect samples of animal carcasses -- vultures' primary food source. In 1990, Nair had analysed vulture tissue samples for pesticides and found 0.485 parts per million (ppm) of dichloro diphenyl trichloroethane ( ddt ) and 0.061 ppm of hexachloro cyclohexane ( hch or bhc ) in the birds' bodies. This time, eight carcass samples were sent for analysis to the Facility for Ecological and Analytical Testing at the Indian Institute of Technology, Kanpur. All samples had high levels of ddt and bhc (see box: Poison in plenty ). Many experts and ornithologists believe that such pesticides may be to blame for the fall in Bharatpur's vulture population.

However, some villagers in Bharatpur allege that the Muslim community is poisoning cattle for their hide. There seems to be little truth in these allegations. Traces of bhc have been found in the carcasses. bhc, till 1997, was legally used for agriculture. Villagers in the area cultivate mustard using large quantities of pesticides. Mustard cake is used as a cattlefeed. Also if the Muslims were indeed poisoning cattle on a large scale, there would have been a riot in Rajasthan. Therefore, deliberate poisoning of cattle on a mass scale seems improbable.

Ornithologists have reported dwindling vulture populations in other Asian countries such as Laos, Cambodia, Vietnam and Thailand, too. "There have been reports that cattle carcasses are now being left unattended (in these countries) due to the absence of vultures," writes Rahmani in his note on decreasing vulture population. Though Vietnam and Thailand banned the use of ddt, hexacyclochlorohexane ( hch), aldrin and other such organochlorine pesticides in 1992 and 1996 respectively, these are still being used there and in the neighbouring countries, including Laos and Cambodia. In India, absence of baseline data makes assessments of such population declines next to impossible, he adds.

There can be several factors behind avian population decline, such as habitat destruction, epidemics, hunting, trapping and the occasional food shortage. None of these could be responsible for such drastic declines as witnessed in Bharatpur, and are secondary causes, believe ornithologists. "Pesticides are probably responsible for the recent decline in vulture and other bird populations in India," says Nair. Residues found in the brain tissues of dead birds indicate that these chemicals could indeed be the killers.

So there is reason to believe that there could be a strong link indeed between pesticides and dwindling vulture populations. Vultures, other birds of prey and humans depend on meat as one of their food sources. So if pesticides are affecting vultures through dead animals, they could get to humans, too. But how do pesticides, sprayed on agricultural fields, affect vultures?And how are humans at risk? The answer, explains Tariq Aziz of the wwf- India, lies in the food chain.

"The food chain is a mode for carrying not only food but also pesticides," he says. "Pesticides find their way into the water where they affect the lower-level organisms. Then, as these are devoured by the other creatures, the chemicals affect them too," Aziz continues. "Intake and effects of the chemicals increase several times along the food chain. Assuming a fish's daily diet is a million planktons -- each already contaminated by pesticides in the water. Now if a human or a bird eats some four-odd fish a day, it will definitely have more of the poison."

Is this decline in vultures an ominous sign? Are these birds like the canaries kept by the 19th century miners? Back then, coal miners would not enter the mines unless they had a canary with them. If the mines had methane inside, the bird would succumb first and the men knew it was time to run. Perhaps, there is a similar message for us in the recent vulture deaths.

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