A characteristic of sick vultures seems to be head-drooping for long periods, with their eyes closed and feathers ruffled. This lasts for about 30-32 days and then the bird simply drops dead.
This lethargic behavior is dangerous for vultures because they need to fly to stay cool. Vultures soar not so much to search for food but to get up where it is cooler, said Cunningham.
Ironically, in the midst of all the vulture deaths, one of the biggest hurdles has been obtaining freshly dead birds for necropsies. Ideally one would just kill a couple of really sick birds, but in India killing any form of wildlife is illegal.
"The pattern of deathsthe same clinical signs all over Indiadoesn't fit the signature of chemical contamination," said Cunningham. Toxicology results have come back negative, showing no significant levels of toxic pesticides or industrial pollutants in any of the dead birds. Searches for various bacterial agents have also produced no results.
"We have tested all the usual suspects," said Cunningham, "and I'm guessing that we are probably dealing with something new." We are as sure as we can be without actually seeing anything that we are dealing with a virus, he said.
In India vultures perform the essential task of carcass disposal.
When cattle die hide collectors remove the skins and leave the carcasses for the vultures. "During the 1980s, 100 to 150 vultures would descend on a single carcass, stripping it to the bone within 20 minutes," said Prakash. "You would never find a carcass in the 80s, only a skeleton. Now the carcasses just rot and stink for days."
Prakash counted cattle carcasses along 8,000 kilometers (5,000 miles) of roadside as he drove between national parks. He found that only five percent of the carcasses had vultures feeding on them, and even then it was just a few birds.
The decline in vulture populations is so dramatic that during nine visits to India within the last two years, Cunningham said he has yet to see a vulture actually feeding on a carcass. "And I've been to places where you would normally see them."
It's the villages across rural India that are most worried because there is no efficient method for carcass disposal. And now the carcass dumps near the main cities are really beginning to stink.
Thousands of carcasses are left to rot at the Bapna processing plant near Bombay, Tonk plant near Jaipur, and the Gazipur plant in Delhi, whereas a decade ago these places swarmed with vultures.
With the void left by the vultures, and abundant carcasses available, populations of fast breeding scavengers like feral dogs, crows, and rats are escalating rapidly.
The population of dogs is increasing at an alarming rate, said Prakash. "At one dump there were more than a thousand dogs feeding on carcasses. These dogs are ferocious, they attack deer and antelope and hunt in wild packs."
Wild Dogs Have Become a Problem
The wild dogs are a particular problem because they spread rabies, which is endemic in India.
So far the disease appears to affect only the Gyps genus of vultures, which include the white-backed and long-billed vultures (Gyps bengalensis and Gyps indicus), the Eurasian griffons (Gyps fulvus) and Himalayan griffons (Gyps himalayansis). Four other species of vultures that are endemic to India seem unaffected but are unlikely to fill the void.
An additional concern is the spread of the disease to vulture populations in other parts of the world. Eurasian and Himalayan griffons are migratory and there is a continuous distribution of these birds throughout Europe and Africa.
The disease has already spread to Nepal and Pakistan.
In the Punjab Province of Pakistan biologist Munir Virani, of The Peregrine Fund in Boise, Idaho, and his colleagues performed about 70 necropsies of adult white-backed vultures71 percent had gout.
"There are still many vultures left in Pakistan but the rate at which the adults are dying does not bode well," said Virani, who surveyed vulture populations in Pakistan and Nepal.
Last year Eurasian vultures were sighted in Kenya for the first time. Although the birds migrate through Africa they have never been seen as far south.
If the disease were to spread to Africa the consequences would be devastating, said Virani.
"In Africa, vultures consume about 70 percent of the ungulate carcasses, not the hyenas and lions," said Virani. "If the vultures died out the consequences would be unthinkable."
In October a team of scientists from The Peregrine Fund met in Kenya to established a vulture monitoring program in East Africa to watch for signs of sick vultures.
Parsi Burial Rites Threatened
One community particularly affected by the decline in vulture numbers is the Parsis. For the past two thousand years Parsis have left bodies exposed to the skies and to the vultures who eat the remains.
"We believe that if we burn our body, we are desecrating fire," said Khojeste Mistree, a Zoroastrian theologian. "If we bury our body, we are polluting the earth. If we drown our bodies we are sullying the water. Therefore, the only method of disposal that is available to us is in fact the natural elementthe sky. So we have an exposure method by the name of Dokme Ni Shini."
For the past 400 years Parsis in and around Bombay have taken their dead to an area of secluded parkland, a 57-acre (23-hectare) hill that was originally on the outskirts of the city but is now surrounded by urban sprawl. Here, on this partially manicured parkland are the Towers of Silence, where the Parsis leave their dead.
The bodies are laid out for the vultures on huge cylindrical stone towers, some up to 300 feet (90 meters) across, and about 20 feet (six meters) high. Until the 1990s the Towers of Silence had proved an efficient way to deal with dead bodies with hundreds of birds perching on the towers.
"I was told that in half an hour the entire body, except for the leg bones would be gone," said Jemima Parry-Jones of The National Birds of Prey Centre in Newent, United Kingdom. Once the vultures had done their part the remnants were swept into a central pit containing charcoal and lime. Over time, sunlight and weather reduced the bones to dust.
But when Parry-Jones visited the towers in 1999 no vultures were seen at the towers, leaving the Parsis community with the rather urgent issue of how to deal with the mounting numbers of dead bodies.
Currently the Parsis are using solar panels to concentrate intense heat on the bodies to help them disappear. But the community is divided on whether their ancient rituals are outdated. Some believe that cremation should replace the tradition of the towers. Others want to erect an enormous aviary over the three largest towers.
The aviary would require about 300 vultures to perform the daily task of removing the bodies. But the idea is fraught with potential problems.
"First we have to find 300 healthy vultures," said Parry-Jones, who has designed an aviary for the towers. "And that is no easy task."
"Nobody has ever put 300 vultures in an aviary beforewe don't know what will happen if these birds are fed exclusively on human flesh," said Parry-Jones. Wild birds have a much more varied diet. And with such a large number of birds extensive maintenance would be required to keep the birds healthy and the aviary looking and smelling clean.
There is also the issue of creating an aviary large enough for the birds to feed, bath, roost, and fly.
"The Parsis have relied on vultures for two thousand years to sort out their dead," said Parry-Jones. "But this community wants to continue an ancient tradition in a modern world without having any understanding of the needs of these birds."
Currently an international team of scientists is collaborating with colleagues at the Bombay Natural History Society to build a captive care center for the vultures at the foothills of the Himalayas, north of Delhi. The team has received a grant from the UK Darwin Initiative for the Survival of Species of 148,000 British pounds (U.S $225,000), to monitor the disease process and test whether the vultures will respond to any treatments.
"The Indian Government could definitely help the Bombay Natural History Society by giving them blanket permission extending throughout the country to continue their research," said Cunningham.
Currently the BNHS must negotiate with each state government to study and collect dead, sick, and healthy vultures for the purpose of taking samples.
"The vulture is such a common bird, and not glamorous, so people do not understand its importance," said Prakash. But without the vulture the ecology of the entire region is out of balance.
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