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What's Ailing Asia's Vultures
by Howard Youth

Were your friends; were your friends were your friends til the bitter end. A gang of British-accented vultures belt out these lyrics in the famous 1960s Disney movie The Jungle Book, an animated musical set in India and loosely based on Rudyard Kiplings fiction, itself only casually inspired by true Indian natural history. Animated vultures with Beatles-like hairdos may not mirror reality, but vultures, secondarily at least, have been our friends. Specifically, they provide natural sanitation services. Nowhere has this been as evident as in India, a country of one billion people that has long been high on human population but stretched on garbage-disposal services. There, vultures scoured the countryside for animal carcasses, and in recent decades fed mightily at large city dumps, as well.

The late, great Indian ornithologists Slim Ali and Laeeq Futehally painted a more realistic picture of vultures at work in their 1967 book entitled Common Birds: The gruesome obsequies at a carcase are attended by incessant jostling and bickering among the feasters and much raucous screeching and hissing as two birds ludicrously prance around with outspread wings tugging and pulling at a gobbet of flesh from either end.

Large numbers of these peacock-sized birds, with an impressive seven-foot wingspan, would circle overhead, seeking fellow vultures, jackals, or other scavengers that might already be busy dismantling a carcass. Soon, the floating prospectors would drop down to join frenzied feedings, covering carcasses with their dusty brown wings and backs. Ali and former Smithsonian Secretary Emeritus S. Dillon Ripley wrote of the white-rumped vulture: A mixed rabble of 60 to 70 birds (mostly of this species, and including a few kites and crows) was timed to strip the skinned carcasses of two sloth bears weighing not less than 275 pounds so thoroughly in the space of about 40 minutes that late comers at this stage had to stand around disappointed. On Mumbais (formerly Bombays) famed Towers of Silence, members of the Parsi religion traditionally left their dead for vultures to pick clean, rather than contaminate sacred earth, water, or fire with their remains. There, a horde of vultures could reportedly reduce a human body to no more than bones in 30 minutes.

In 1992, while visiting northern India, I saw Indias commonest vultures, the white-rumped (Gyps bengalensis) and long-billed (Gyps indicus), gorging on cow carcasses in fields off the highway approaching one of the worlds most famed bird reserves, Keoladeo National Park (also called Bharatpur). At the park, the black backs and whitish neck of white-rumped vultures identified these birds as they sat on bulky stick nests in the shade trees, overlooking wetlands that teem with nesting spoonbills, painted storks, and herons. Nearby, the long-billed vultures, dusty brown with darker brown wings, looked much more drab.

Today, the Disney song rings a bit truer: many wonder if the birds bitter end is near. Less than ten years after my visit, two of Indias most common and familiar birds are listed as critically endangered and both are virtually gone from the park. Birds once described by Ali as sailing majestically for hours on end on outspread motionless wings sit stoop-necked and still for days before falling out of trees, dead. Vultures no longer soar over Mumbai and for about two years none have visited the Towers of Silence. Now, followers of the Parsi faith employ strong solar panels that desiccate and hasten the decomposition of their dead in a way that does not forsake their beliefs. A recent survey in Keoladeo National Park, where as many as 350 white-rumped vultures nested in the late 1980s, found none there; this, in spite of the fact that there are an estimated 4,000 suitable tree-nesting sites. More than 800 long-billed vultures were also counted there in the late 1980s, but only one was found during the 1999 to 2000 survey.

Fearing the Domino Effect

Throughout the world, scientists are scratching their heads as to why, since about 1997, vultures of the genus Gyps are vanishing from India, and more recently Pakistan and Nepal. The words crash and catastrophic are frequently used. Surveys done in 2000 revealed greater than a 90 percent decline for these two species in various protected areas, along roadways, and in surrounding country. Although the birds remain in small numbers in some areas, theyre totally gone from many others. Overall, no one disputes the fact that across the subcontinent, the birds are declining.

At first, scientists worried that widespread pesticide use, which is on the increase in the region, poisoned the birds. Many believe that declines in many Indian bird populations, from those of bee-eaters to raptors, may be due to rampant pesticide applications. In India, organophosphates, such as malathion, and pyrethroids, like fenvalerate, are commonly used and residues of DDT, dieldrin, and other organochlorine pesticides have been found in vulture tissue samples. These pesticides can and do harm birds and other wildlife. Scientists at The Peregrine Fund, an Idaho-based organization focused on global raptor conservation issues, is investigating the die-off on several fronts, including the pesticide angle. We feel that it is important to consider all possible alternatives that might explain such heavy losses, and so have devoted a significant portion of our efforts on a survey of chemical use in rural Punjab [in Pakistan], says Martin Gilbert, a field veterinarian working for the group.

Because the puzzling vulture declines have been so widespread and limited to vultures of one genus, sleuths also look in another direction for clues. In September 2001, the fourth annual Eurasian Congress on Raptors, convened by the Raptor Research Foundation in Seville, Spain, showcased global vulture conservation issues. The Indian crisis was a major focus. Researchers from the Bombay Natural History Society (BNHS), The Peregrine Fund, and other groups shared results of their preliminary studies in India, Pakistan, and Nepal, and agreed that their work had only just begun. Although further study is necessary, many scientists now believe an infectious disease, possibly a virus or bacterium, is at work.

As yet, no one has been able to demonstrate that the vulture mortality relates to an infection, and so we have undertaken work aimed at demonstrating transmission of the condition from one bird to another, says Gilbert. Gilbert and Peregrine Fund biologist Munir Virani, working with the Ornithological Society of Pakistan, monitor breeding activity and mortality at three study sites in the Punjab region, one of which adjoins the Indus River, which marks the current front line of the die-offs. All three sites have declining populations. One particular site has shown an 80 percent reduction in the number of breeding pairs in a single year, says Gilbert. Mortality rates continue to be high, consistent with a very rapidly declining population. During just the 200102 breeding season, the two scientists collected 180 dead vultures. They send tissue samples to Lindsay Oaks, a Washington State University pathologist, who conducts diagnostic tests on them. So far, 90 percent of the birds necropsied show signs of visceral gout, an indication of renal failure. Scientists analyzing dead vultures in India found similar symptoms.

Some suspect that the vultures kidneys fail after severe dehydration that occurs because lethargic, sick birds dont drink for days. But diagnostic tests done by The Peregrine Fund and its partners on vulture carcasses in Punjab Province in 2000 and 01 suggested that there is a disease selectively affecting the kidneys (directly or indirectly) of adult and sub-adult vultures resulting in sudden death. A new bacterium was detected in the lungs and spleen of several vultures. The potential significance of this organism to the kidney disease and vulture die-off is under investigation. Meanwhile, other investigators with the British Royal Society for the Protection of Birds (RSPB), the BNHS, the Institute of Zoology (London, England), and other organizations are also working to find out if some sort of illness is killing the vultures.

So far, scientists have not been able to treat sick vultures; most of those found have been dead. Thus there has not been an opportunity to provide therapy, says Lindsay Oaks. Only a handful of sick vultures have been found while still alive, and these were in the terminal stages and died shortly after capture. Meanwhile, in Indias northwestern state of Haryana, RSPB and BNHS scientists, collaborating with other groups, recently set up a center for caring for sick vultures and those not yet afflicted. The hope is to learn and treat this illness.

Of nine species of vultures in India, only the five in the genus Gyps seem affected by the illness, but these far-wandering birds seem to be spreading the mysterious affliction farther and farther west. If the die-offs continue to march westward, there could be a domino effect in Gyps vulture populations that extends far beyond Asia. In the end, eight of the worlds Gyps vulture species might be affected, compromising the abilities of these birds to clear their habitats of rotting dead animals.

Since the 1960s, biologists have noted the decline of white-rumped and long-billed vultures in countries east of India. In 1953, Bertram E. Smythies wrote in The Birds of Burma that the white-rumped vulture was still found throughout the countrys plains and that the long-billed vulture, although less common, was found through much of Myanmar (formerly Burma). Today, there have been no recent sightings of long-billed vultures in Myanmar, although some were recently reported in Laos and Cambodia. The species is now considered extinct in Thailand and Malaysia. The more widespread, and once abundant, white-rumped vulture now occurs spottily east to Vietnam, but is basically gone from most of Asia east of India. Both of these species likely declined because few large animal carcasses were available in settled landscapes where the people eat meat. During that time, however, Indias vulture populations increased. There, the Hindu majority revered cows and millions roamed villages, cities, and countryside. Other livestock, especially bullocks (castrated bulls) and domesticated water buffalo, were employed as beasts of burden. Thus, a steady supply of carcasses was assured.

While vulture declines east of India took place before the current die-offs, scientists cannot fully dismiss disease, which might have struck from the east and slowly moved west into India and Pakistan, hitting the core populations of these species, including large concentrations that assembled at human-supplied dumps and livestock-carcass dumping grounds. Gyps vultures feeding in the countryside also crowd together, says Bob Risebrough, a biologist specializing in contaminants effects on wildlife. Surely, however, the very large assemblages [at dumping grounds] would have hastened the transmission of a disease factor.

Other scavengers appear to be taking over the vultures important places in India. Reportedly, populations of feral dogs, rats, and crows are exploding in the absence of the ravenous and fast-eating vultures. While Indians usually leave nesting vultures unmolested and the birds, for their part, never attack people, feral dogs pose less peaceful prospects, traveling in dangerous packs that could attack people and transmit rabies to them. Recently, more than 1,000 dogs were counted at just one carcass dump in the northwest Indian state of Rajasthan. With a rise in less desirable scavengers, the lowly vultures suddenly seem far more appealing to people who never gave them much thought.

Similarities and Differences

While many of the worlds vultures nest in wilderness areas, Indias vultures often nest in or around villages or cities. White-rumped vultures will set up their loose platform of sticks in shade trees in towns or along roads. Breeding takes place in the cooler, drier months, between October and March, and pairs indulge in courtship soaring to cement pair bonds.

Based on a study recently conducted by Smithsonian ornithologist Pamela Rasmussen, the long-billed vulture is now widely regarded as not one, but two species that vary in numerous morphological aspects, distribution, and nesting habits. The recently split species may look similar but, among other things,Gyps tenuirostris ranges from the lower Himalaya eastward, while Gyps indicus is found south of the River Ganges in India and west to a bit of eastern Pakistan. The Himalayan birds build more compact nests in trees, often near human settlements. The southern and western birds build looser nests on cliffs or old hilltop fortresses. Meanwhile, the white-rumped vulture nests in trees, usually near people and not far from a favored source of dead cattle.

The long-billed and white-rumped vultures usually lay just one egg. Males and females share nesting duties, doing shifts during incubation, which lasts 45 days. It takes young about three months to leave the nest. As slow breeders, these vultures are especially vulnerable to population declines. During the current crisis, many sick adults die before their young fledge, leaving them to starve.

Old World Foul

Old World vultures, including members of the genus Gyps, are far different fowl from the turkey and black vultures that nature lovers admire in and around the Washington area. Taxonomists place the 15 vulture species of Europe, Africa, and Asia within the family Accipitridae, which includes eagles, hawks, kites, and harriers. New World vultures, including turkey and black vultures and California and Andean condors, fall within their own family, the seven-member Cathartidae. Many behavioral and morphological distinctions set the two families apart, although superficially both sets of vultures appear similar. In fact, they were long considered in the same family. Today many taxonomists believe that New World vultures are more closely related to storks than to other birds of prey. The similarity between Old and New World vultures is now chalked up to convergent evolutionthe process by which unrelated creatures that occupy similar niches in different places come to resemble each other over time. For instance, the worlds vultures, regardless of family, generally have sparsely feathered heads and necks, allowing them to tear into carcasses then easily wash off afterward, and they lack strong talons characteristic of most other raptors.

The suddenness and scope of the Asian vulture die-offs raises far more questions than there are answers. Did the birds contract and spread illness due to unusually large concentrations of birds? Are enough vultures still surviving and breeding to allow the species to survive? How many species will be affected and how far west will the die-offs spread? If mortality continues to be high, the first likely candidate for extinction could be the recently split Himalayan long-billed vulture. Fieldwork conducted last season in Nepal by The Peregrine Fund and Birdlife Nepal were able to locate only two nests of the species, says Gilbert.

There are few comparable examples of such widespread, mysterious losses among birds. Most involve island birds, which had no immunity to introduced illnesses, predators, or competitors. The Hawaiian islands provide a showcase example: There, introduced mosquitoes feeding off introduced birds spread avian pox and malaria to the islands native birdlife with disastrous results. Today, most Hawaiian honeycreepers and the critically endangered Hawaiian crow survive only in mountain forests, fading away as mosquitoes reach higher and higher altitudes. No one really knows if the vulture die-offs are due to an infectious disease, but its easy to ask what if?

Hawaii is a classic example of avian populations reduced through introduction of novel disease, says Gilbert. The important distinction is that this has involved small populations of island species. The potential extinction of a continental species with a population declining from numbers in the six-figures range is something quite different. Although up to 90 percent of avian extinctions since 1600 occurred on islands, some once-abundant continental birds also vanished entirely, due not so much to disease as to habitat loss and huntingfactors not affecting the vultures. These include the Carolina parakeet, the great auk, and the passenger pigeon, although the passenger pigeons demise was likely exacerbated by an outbreak of Newcastle disease, an illness that affects both poultry and wild birds. There has been no extinction in recent history that compares with what we may now be seeing in the vultures, says Gilbert.

Gilbert and Oaks both clarify that no one yet knows if a disease is responsible, nor whether any extinctions will occur. A few years back, biologists thought they might have to set up a captive breeding program for vultures to ensure that at least some unaffected birds survived and bred. Now, based on reports from biologists and birders in the field, it appears that some vultures are still successfully breeding or even returning to remote parks and even Indias sprawling capital New Delhi, where at least a few pairs still nest. Some birds therefore appear to have escaped exposure, or were sufficiently resistant, says Risebrough. At the moment the possibility that they had sufficient genetic variability to include an inherited resistance is just speculation. The reports of small groups of survivors decrease the urgency, but do not eliminate the necessity of creating captive, disease-free flocks. The immediate priority would be to obtain data on the nesting success of these surviving birds, he says.

Reports of small numbers of breeding pairs in India may indicate a heavily reduced population that is resistant, and thus, hopefully, able to recoveror alternativelymay remain susceptible, and represent the last of the species, says Gilbert. Seeing a vulture soaring is like watching an entirely different species from that which tugs at bloated carcasses. Though a repulsive creature at close quarters, wrote Ali, a vulture gliding majestically in the sky on outspread motionless wings looks the embodiment of grace and buoyancy. While no one can fully predict the final outcome of the vulture decline, its hard not to fear for the future of the worlds most famed scavengers, which would leave our world less rich and balanced if they were to reach their bitter end.

Howard Youth writes from Madrid, Spain, near the western extreme of the Eurasian griffons breeding range. There, free from the mysterious illness, the birds are on the increase.

ZooGoer 31(4) 2002. Copyright 2002 Friends of the National Zoo. All rights reserved.