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Mystery Disease Stalking Vultures in Asia |
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Bijal P. Trivedi National Geographic Today |
| May 20, 2003 |
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This week in Budapest, Hungary, an international gathering of scientists will explore how to save a creature that itself symbolizes doom: the vulture. At the 6th World Conference on Birds of Prey and Owls, several sessions will focus on the Oriental white-backed vulture, Gyps bengalensis, once the most common bird of prey in Asia and possibly in the world. Vultures used to be as numerous as "pigeons in cities of the United States," says Rick Watson, a raptor ecologist and director of international programs at the Peregrine Fund in Boise, Idaho. During the last decade, populations of bengalensis, and the Indian and slender-billed vultures—Gyps indicus and Gyps tenuirostris, respectively—have declined by more than 90 percent in India. Scientists believe that the cause is infectious disease, though no one has identified the pathogen. Now new research by Peregrine Fund biologists show that at some sites in Pakistan the birds are also disappearing rapidly. "We are losing up to one third of the adult population each year—about three to seven times the normal rate for a raptor population," says Watson. "At this rate bengalensis is well on its way to extinction." Vultures play an essential ecological role as garbage collectors and recyclers. They rid the environment of carrion, which breed diseases—including anthrax. In Africa, for example, vultures consume more than 70 percent of zebra, wildebeest and other hoofed animal carcasses—not lions or hyenas. "The Gyps vultures depend exclusively on livestock in India and Pakistan—without them there would be an incredible number of dead animals rotting over the countryside," says Munir Virani, a biologist with the Peregrine Fund's Asian vulture crisis project. Investigating the Disease In the Changa Manga forest in Pakistan's Punjab province, researchers say that their vulture study may be over—not because they have solved the mystery of what has decimated the population, but because no more vultures remain. At Changa Manga the number of active nests has fallen from 198 in 2001 to 49 in 2002 to just six in 2003—a decline of 97 percent, says Virani. Similar declines have been recorded at sites throughout India, Nepal and Pakistan. About nine species of vultures live in the Indian subcontinent, and each has a specific ecological role. Packs of wild dogs and rats are slowly filling the void left by bengalensis vultures. In a remote forest region about ten miles from Chandigarh, India, in the foothills of the Himalayas, researchers have just opened a Vulture Care Center. There they will care for sick vultures and try to identify what's killing these species. The center maintains labs, large aviaries and individual "hospital" aviaries for sick birds that will be monitored by closed-circuit television—an unobtrusive way to monitor the people-shy birds. When ill, the birds droop their heads and progressively become more lethargic. "In captivity, the sick birds will not droop their necks if watched (by people), it's a protective technique so that they don't look vulnerable," says Andrew Cunningham, head of wildlife epidemiology at the Zoological Society of London. After several weeks of "drooping head behavior," the birds die of so-called visceral gout—a buildup of uric acid crystals, a natural waste product, particularly in the heart, liver, and kidneys. Nobody knows what causes the gout but researchers suspect a new virus. "These birds are dying from an infectious disease," says Cunningham, "dehydration and gout is just the end stage." Satellite Studies, Disease Spread At the vulture care center, veterinarians will monitor how the disease progresses in sick vultures, and take frequent blood samples—something that hasn't been possible in the wild. They will also harvest tissue samples immediately after a bird dies. Until now, these samples were taken from dead animals stumbled on by researchers at study sites after the corpse had been sitting the sun. Often the tissue was unfit for study. "In those conditions the virus would die along with the animal and we wouldn't have any chance of discovering it," says Cunningham. A danger is that whatever is plaguing the vultures may spread to other species. Researchers are monitoring the highly migratory Eurasian vulture species that winters in India. In January, Indian and British scientists launched a pilot satellite tagging program to find out where the Eurasian vulture breeds and where it migrates. The team, led by Debbie Pain, a biologist and head of international research at the Royal Society for the Protection of Birds, tagged four healthy vultures—two Eurasian and two Himalayan—near the vulture center. "Within two weeks the Eurasian vultures had crossed China and ended up in Mongolia, traveling a total distance of more than 1,600 miles," says Pain. "We had no idea they traveled so far so fast." The Eurasian vulture is within the same genus of vulture as bengalensis. Cunningham and Pain fear disease transmission from India into Africa via the Middle East. "There could be very severe ecological consequences in Africa if vultures decline," Pain says. In October the researchers will begin a surveillance and satellite tagging project for the Middle East—Jordan, Yemen, and Iran—to monitor for the appearance of the disease there. The Budapest meeting may just expedite their efforts. 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