Silent towers, empty skies
|©Munir Virani/The Peregrine Fund|
On the round-the-world trip chronicled in his book Following the Equator, Mark Twain stopped off in Bombay (now known as Mumbai) and, as part of the standard tourist circuit, was taken to the Towers of Silence, where the Parsi community brought their dead. "On lofty ground, in the midst of a paradise of tropical foliage and flowers, remote from the world and its turmoil and noise, they stood," Twain wrote. "The vultures were there. They stood close together in a great circle all around the rim of a massive low tower - waiting; stood as motionless as sculptured ornaments, and indeed almost deceived one into the belief that that was what they were."
The assemblages Twain saw are a thing of the past. The vultures have vanished from Mumbai, and populations of three vulture species have nosedived all over the Indian subcontinent: India, Pakistan, Bangladesh, Nepal. The die-off has had profound consequences for public health, as well as for Parsi funerary practices. Biologists at first suspected an infectious agent and feared migrating vultures might spread it to the savannas of Africa. But research in Pakistan by The Peregrine Fund points to an unsuspected cause: an anti-inflammatory drug called diclofenac sodium, widely used in veterinary as well as human medicine."This is the first known case of a pharmaceutical chemical involved in damage to a wildlife population," says toxicologist Robert Risebrough, who has studied the effects of toxics on California condors and other endangered birds, and has made several visits to India to investigate the vulture die-off.
The relationship between humans and Old World vultures is an ancient one. Long before the rise of Homo sapiens, hominids likely tracked the scavenging birds to locate the kills of more adept predators. Eight thousand years ago, the inhabitants of the Neolithic city of Çatal Hüyük in Anatolian Turkey appear to have exposed corpses to be stripped of flesh by vultures as part of the preparation for burial. If, as some archeologists and linguists believe, Anatolia was the homeland of the Indo-European language family, the Parsi practice may have its roots there.
India's Parsis follow a religion founded by the prophet Zoroaster around 1400-1200 BCE on the Asian steppes. His disciples were a nomadic people, speaking a tongue ancestral to modern Farsi, who moved south into present-day Iran. The state faith of successive Persian empires, Zoroastrianism was brought to India in 936 AD by refugees fleeing persecution by Arab Muslim conquerors. Holding earth, fire, and water too sacred to pollute with corpses, Zoroastrians relied on wild scavengers to dispose of their dead. A text from the time of the Parthian Empire, contemporary with Imperial Rome, directs believers to leave a body "on the highest places, so that corpse-eating beasts and birds will most readily perceive it." Simple platforms for exposure were later replaced by open-topped stone structures called dakhmas; "Towers of Silence" was the coinage of a 19th-century British journalist.
The dakhmas of Mumbai attracted the once ubiquitous white-rumped or Indian white-backed vulture (Gyps bengalensis). A mid-sized vulture with a wingspan approaching seven feet, the white-rumped inhabited the region from southeastern Iran to Vietnam and Cambodia. In India, it could be found wherever carcass dumps, slaughterhouses, or bone mills provided a food source. With the agricultural development of western desert regions under the British Raj, the white-rumped spread into Sind, Punjab, and Rajasthan. It's a gregarious bird, often nesting colonially and feeding in quarrelsome flocks.
Its close relative, the long-billed vulture (G. indicus), was also abundant through the western portion of the white-rumped's range, outnumbering it in peninsular India. A third form, the slender-billed (G. tenuirostris), once considered a subspecies of the long-billed, differs in bill structure and nesting habits; it occurred in smaller numbers from Kashmir through Bangladesh to Southeast Asia.
No one attempted a vulture census before the declines began. It's estimated, though, that white-rumped vultures numbered in the millions in India and neighboring countries, and long-billed vulture populations ran at least to six figures. They were far more numerous than other scavengers like the red-headed and Egyptian vultures and the black kite. A survey of the status of birds of prey in India in the 1980s reported that none of the species was in trouble, and there was no reason then to anticipate a decline. Except around airfields, coexistence with humans was not a problem, and the supply of cattle carcasses was endless.
Mohandas Gandhi once explained why, as he put it, "the central fact of Hinduism" was the protection of the cow: "The cow was in India the best companion. She was the giver of plenty. Not only did she give milk but she made agriculture possible." Most of India's states legally mandate protected status for cattle, and the demand for such legislation in the holdout states of Kerala and West Bengal has touched off riots and protest fasts. In The Sacred Cow and the Abominable Pig, anthropologist Marvin Harris described how Hindus "venerate their cows (and bulls) as deities, keep them around the house, give them names, talk to them, deck them with flowers and tassels, let them have the right of way on busy thoroughfares, and try to place them in animal shelters when they become sick or old and can no longer be cared for at home."
As of 1997, India was home to an estimated 197 million cattle. Though some are eaten by Muslims, Christians, and lower-caste Hindus, millions die every year of natural causes. Even with competition from feral dogs, corvids, kites, and other scavengers, that was enough to support healthy numbers of vultures.
Within the last decade, though, observers suddenly realized that something was happening to the birds. Biologist Vibhu Prakash was one of the first to sound the alarm. Beginning in 1985, Prakash worked in Rajasthan's Keoladeo National Park, where white-rumped vultures nested and long-billed vultures came to forage from nearby breeding sites. He saw the numbers of the park's white-rumps go from a peak of 1,800 in 1985-86 to only 86 in 1998-99, while long-bills fell from 816 to 25. No white-rumps nested in the park in the 1999-2000 season. He reported what appeared to be symptoms of illness: "Prior to death," he wrote in a 1999 article for the Journal of the Bombay Natural History Society, "individual vultures were seen perched on trees, dozing, with the neck slowly slumping down. They would wake up with a start, when the beak hit the branch." Prakash observed five vultures that fell off their perches and died after more than 30 days of neck-drooping behavior.
Prakash ruled out starvation as a source of mortality, as carcasses of cattle, buffaloes, and wild game were still abundant, and he considered deliberate poisoning improbable. He speculated about organochlorine pesticides, heavily used in Indian agriculture, but noted that fish-eating birds in the park appeared unaffected and that the vultures' symptoms were atypical for pesticide contamination. That seemed to leave disease as the most likely explanation. Disease also seemed consistent with the behavior of long-billed and white-rumped vultures, highly social birds that congregate in flocks to feed, making transmission of a pathogen from bird to bird easier. The more solitary red-headed and Egyptian vultures seemed unaffected.
It soon became clear that the vulture crash was not confined to Rajasthan. At a conference in January 2001, observers from all over India told the same story. Long-billed vultures had disappeared from two sites in Maharashtra over six years of monitoring. Numbers at a carcass dump in Uttar Pradesh fell from 6,000 in 1991-92 to five in 1994. Similar accounts came from Punjab, Bihar, West Bengal, even Nepal, where white-rumped vultures had been extirpated in Chitwan National Park.
Alarmed by the catastrophic decline of the two common species and the rarer slender-billed vultures, scientists tried to confirm whether a disease was responsible. There was no shortage of vulture remains for analysis. Post-mortems of birds from Rajasthan, Punjab, and Nepal showed visceral gout, an end-stage reaction to kidney failure. But this could have resulted from either disease or poisoning.
In India, the search for the cause was stymied by an ironic instance of the Law of Unintended Consequences. The controversy over biopiracy - the appropriation by multinational corporations of local biological resources - had been building since the 1980s, when a pesticidal extract from the neem tree was patented by US timber importer Robert Larson. Larson sold the patent to W.R. Grace & Co. in 1988. The neem, with myriad traditional medical uses, became a potent symbol of resistance to corporate rapacity for activists such as Vandana Shiva. Their defense of indigenous knowledge led to the Indian Parliament's passage of legislation prohibiting the export of genetic material. British and American scientists were frustrated to find that this included tissue samples from dead vultures.
British scientists and conservationists Andrew Cunningham of the Zoological Society of London, Deborah Pain of the Royal Society for the Protection of Birds, and Jemima Parry-Jones of the National Birds of Prey Centre continued to work with Indian counterparts. A treatment and research center was established at Chandigarh earlier this year, with Vibhu Prakash as coordinator. Parry-Jones met with representatives of the Parsi community to discuss building aviaries in Bombay. Although other expedients had been used - such as solar concentrators, which desiccate but do not incinerate bodies; Zoroastrianism forbids cremation - Parsi traditionalists wanted to maintain the vultures' historic role. "The Zoroastrian religion cannot be bargained with," Parsi spokesman Khojeste Mistree told a reporter.
Meanwhile, Cunningham performed more post-mortems. At a conference in Seville in September 2001, he reported that many of the birds showed perivascular lymphocytic cuffing, "commonly associated with infection by a viral agent." But he acknowledged that no virus had been identified.
While Cunningham remained active in India, researchers from The Peregrine Fund began to focus on Pakistan, which lacked comparable restrictive legislation. Lindsay Oaks, a veterinary scientist at Washington State University and part of The Peregrine Fund's team, made his first trip to Pakistan in November 2000 and collected dead vulture specimens from several colonies in the Punjab, where heavy losses had also been recorded. By last July, 135 Pakistani vultures had been examined; 77 percent had signs of renal failure. In one specimen, the team also discovered a pathogen related to the mycoplasma that commonly afflicts house finches in the US. The others, however, had no trace of viruses or bacterial pathogens, and no lesions that would have resulted from inflammation.
Other field data questioned the symptoms of whatever was killing the vultures. Vibhu Prakash had considered head-drooping a precursor to death. But Peregrine Fund studies in Pakistan documented an increase in head-drooping from March through May without a concomitant spike in mortality. April, May, and June are the hottest months of the year there, and drooping also seemed to correlate with the day's highest temperatures. Could it be a form of thermoregulation, not a sign of sickness? Head-drooping was also noted in apparently healthy vulture populations in Europe and Africa.
Until this spring, though, no one had come up with a plausible alternative to the disease theory. What made that explanation particularly troubling was the threat that the disease might spread to other continents. The Eurasian griffon vulture (Gyps fulvus) nests from Spain to northwestern Pakistan; some winter in India, but most migrate to sub-Saharan Africa. If griffons carried the infectious agent to Africa, Pain told a reporter, "We will be in real trouble." (The status of Pakistan's Eurasian griffons is unclear, since the provinces bordering Afghanistan are not hospitable to researchers.)
Then in May, at the Sixth World Conference on Birds of Prey and Owls, in Budapest, Oaks dropped a bombshell. The Peregrine Fund research team's Pakistani specimens had tested positive for diclofenac sodium, a nonsteroidal anti-inflammatory drug frequently given to cattle in the Indian subcontinent. "I believe that we certainly have compelling evidence implicating diclofenac as the primary cause of mortality in adult vultures in Pakistan," Oaks told Earth Island Journal. The drug can be toxic even in small quantities and has been linked with kidney damage in human subjects, and a recent study by Sidhartha Ray of Long Island University found that it caused massive programmed cell death in the kidneys of mice.
Bob Risebrough agrees with Oaks. He says that diclofenac is commonly used in veterinary medicines in both India and Pakistan. Although there's no way to verify it now, Risebrough also thinks human diclofenac use may be implicated in the disappearance of the vultures that frequented the Parsis' Towers of Silence. Like other medications, diclofenac is aggressively marketed by the Indian pharmaceutical industry and is widely dispensed by pharmacists without a doctor's prescription. Two years ago, Wall Street Journal reporters Daniel Pearl (subsequently murdered by extremists in Pakistan) and Steve Stecklow documented widespread abuses. Of particular interest is the case of a Mumbai businessman who took the drug, purchased over the counter, for leg pain - and sustained permanent kidney damage. According to Pearl and Secklow, the medication was sold to druggists by Mumbai-based J. B. Chemicals & Pharmaceuticals Ltd. "under a buy-nine-get-one-free scheme."
Following Oaks' announcement, Andrew Cunningham told a reporter for Nature that, at least in India, he still considered an infectious agent the prime suspect. He mentioned the signs of inflammation found in post-mortems and noted that Indian vultures seem to go through a prolonged illness while Pakistani vultures die suddenly. Oaks declined to comment on Cunningham's claims, since the British team's research results have not yet been published. (Cunningham is currently traveling and did not respond to my e-mail.) One wonders if Cunningham still considers head-drooping a reliable pre-morbid symptom. As Munir Virani of The Peregrine Fund pointed out at the Seville conference, sick vultures may droop their heads but not all head-drooping vultures are necessarily sick.
If Oaks is right about diclofenac, the nightmare scenario of migrant vultures spreading a disease from Asia to Africa can be dismissed. But confirming the drug as the cause of the population crash would raise new political challenges. "Is it possible to ban a medicine with so many companies profiting from it?" asked Risebrough. The answer may be a cautious yes. "There are powerful public health reasons for having all those [cattle] carcasses consumed," he went on. "With competition from the vultures removed, feral dogs are multiplying and spreading rabies." The vultures, in short, may have a broader constituency than just the ornithologists and the Parsis.
Risebrough is heading back to India to confer with other researchers and visit potential captive-breeding facilities. The most urgent candidate for triage is the slender-billed vulture, never as common as the white-rumped or long-billed. Only a few hundred remain, some in India's Assam state and a disjunct population in northern Cambodia. Risebrough says there are currently no slender-bills in captivity. "These species may well just have to exist in zoos for a while," he said, noting that the Chandigarh research site could be used for captive breeding. He says breeding vultures are being followed throughout their nesting season in Pakistan and Nepal, and comparable field data are urgently needed from India.
Bringing back the Indian subcontinent's vultures will clearly be an uphill struggle. But it's a critically important one, involving vital ecosystem services. If the political will exists, India and its neighbors may be able to keep their airborne sanitation crew on the job.
Joe Eaton is a freelance nature writer based in the San Francisco Bay Area.