UPDATE - January 28, 2004 - Asian vulture die-off solved. It's caused by a diclofenac, a painkiller commonly fed to cattle, and not by a disease. [Initial report of findings dated 20 May 2003.]

UPDATE - November 2002 - VultureDeclines.org - new website

"Threats to the Vultures of Asia, the Middle East, Europe and Africa, and Strategies for an international Action Plan," Abstract and Summary of the Recommendations, by Robert W. Risebrough & Munir Ali Virani

"Very recent Vulture situation in Pakistan," by Robert W. Risebrough

Population Crash of the Gyps Vultures in India

Evidence for a disease factor and recommendations for emergency efforts.

by Robert W. Risebrough
Berkeley, CA, USA

8 January 2000

A Report to

The US Fish & Wildlife Service
Office of International Affairs
Arlington, VA, USA
Attn: David Ferguson

Copied to:

The Bombay Natural History Society
Mumbai, India
Attn:
Dr. Asad Rahmani, Director
Dr. Vibhu Prakash, Principal Scientist

The Royal Society for the Protection of Birds
The Lodge, Sandy, Bedfordshire, UK
Attn: Peter Wood

THIS REPORT MAY BE DISTRIBUTED TO ANY INTERESTED PERSONS

Summary

Over the past 3-5 years, populations of the white-backed vulture, Gyps bengalensis, and the long-billed vulture, Gyps indicus, over much of India have fallen to less than 5 % of their former abundance; dead vultures continue to be found, indicating that the decline is continuing. A national workshop convened in Mumbai in August 1999 by Dr. Asad Rahmani, Director of the Bombay Natural History Society, confirmed the magnitude and geographical extent of this unprecedented event. A number of possible causes were discussed at the workshop. Among these, two have continued to receive serious attention. The first proposes that a toxin, whether a new pesticide, a familiar pesticide applied in a new way, or another poison deliberately applied to carcasses for whatever purpose has been killing large numbers of vultures, accounting for the population decline. The second hypothesis proposes the appearance of a new disease factor. The liver and other internal organs of three birds found dead or dying in widely separated localities in late 1999 were covered with whitish crystals assumed to be uric acid, deposits of which cause gout in humans. This condition could result from the effects of either a slow-acting toxin or a lingering disease; abundant fat deposits in the abdominal cavities of at least two of the birds indicate, however, that food shortage did not contribute to their deaths.

A review of the effects of toxins on wildlife populations, whether deliberately or incidentally applied, indicates that the probability of a toxin accounting for a population decline of this extent and magnitude is very low. A pattern of reproductive failures observed by Dr. Vibhu Prakash at Bharatpur, consisting of a combination of building nests but failure to lay, the production of eggs that do not hatch, and the death of all chicks hatched from the remaining eggs, indicates a type of sublethal impairment that has not been previously observed and documented as a contaminant effect. The appearance of a new disease factor, presumed to be but not necessarily a virus, which may have ‘jumped’ from another species and which may in turn infect other species, must therefore be considered the plausible working hypothesis at this time. The observations of Dr. Prakash suggest a long incubation period during which sublethal effects are not apparent from casual observations, followed by a period in the order of a month during which the birds show symptoms of sickness, after which they invariably die.

The proposed responses: 1) look for and characterize any disease factor, on an emergency basis; 2) if found, determine relationships with other disease factors to establish a probable origin and mode of entry into the vulture populations; 3) investigate the possibility of transmission to other species, including people. The recent identification in the USA of a virus of African origin that has produced deaths both of people and of wild birds provides an additional rationale for paying close attention to any possibility of a new disease factor in any species; 4) without provoking any undue alarm, public health authorities both in India and in other countries should be alerted to the probability that a new disease factor has appeared in the environment; 5) field studies of surviving birds in both the areas so far affected and areas apparently not yet affected. Emphasis might be placed on studies of reproductive success rather than on censuses; 6) to ensure survival of the two species, continued isolation of any birds that have been in captivity, and the capture and prolonged quarantine of birds from isolated populations; 7) surveys for the presence of disease in other species, particularly crows which frequently share carcasses with vultures. There have been several recent reports of dead crows in the vicinity of Bharatpur and Agra.

Forward

This report to the Office of International Affairs of the U.S. Fish & Wildlife Service, which sponsored my recent trip to India and which has been sponsoring several multi-year studies of raptors in India by the Bombay Natural History Society (BNHS), is a revision and an update of an interim report prepared in Mumbai in December 1999. It is an undisguised attempt to persuade several laboratories anywhere in the world to look for and to characterize, if found, a disease factor that appears to be responsible for an unprecedented population decline of two species of vultures in India that until very recently were very abundant.

The magnitude and extent of this event might be compared with the earlier disappearance of the peregrine falcon as a breeding species in eastern North America. In 1962 rumors circulated among the participants of the International Ornithological Congress in Ithaca, New York, that peregrine falcons were no longer producing young; the blame was, unfairly it turned out, attributed to falconers. A year later, Derek Ratcliffe reported that many traditional nesting sites in Britain were no longer occupied. Joseph Hickey, Professor of Wildlife Ecology at the University of Wisconsin, who in 1942 had published a now-classic paper on the distribution of peregrine falcons in eastern North America, a paper that confirmed the long-term population stability of this species, immediately saw a possible link with the rumors of problems in the North American population that continued to circulate among American ornithologists, bird-watchers, and falconers. In 1964, with the assistance of a private financial donor, he sent Daniel Berger and Charles Sindelar to census all known nesting sites east of the Mississippi River. None were occupied by peregrines; peregrine falcons had become extinct as a breeding species in eastern North America without the knowledge of the ornithological community. The following year Professor Hickey convened a conference in Madison, Wisconsin, that examined in detail all possible causes of this remarkable and unprecedented event. Many were proposed, including the disappearance of the passenger pigeon which had been a traditional food species, radioactive fallout from the weapons testing programs, the advance of civilization and the resulting disturbance, disease factors, and effects of the chlorinated hydrocarbon class of pesticides that had come into widespread use since the 1940s. In the absence of sufficient information, however, it was not possible to reach any conclusion about which was or were responsible.

In August 1999, Dr. Asad Rahmani, Director of the Bombay Natural History Society, brought people from all over India to Mumbai to discuss the decline of vulture populations and the possible causes. Many were proposed, just as 34 years earlier, many different possible causes had been proposed to explain the disappearance of the peregrine falcon in eastern North America.

Again, it was not possible to reach a conclusion about which was most likely the cause.

The 1965 conference in Madison stimulated a wide variety of research programs in institutions of several countries. Four years later, the principal responsible cause was determined with reasonable scientific certainty. DDE, a derivative of DDT, was shown to affect the eggshell structure of a number of bird species, resulting in the breakage of eggs or their failure to hatch. It was a thoroughly unanticipated and unpredictable effect of a new technology.

In the late 1960s and early 1970s I was privileged to participate in the campaigns to end all unnecessary uses of DDT, - in North America at that time that meant all uses of DDT, - and to phase out at the earliest possible time all uses of the polychlorinated biphenyls (PCBs). Scientific credibility was the critical ingredient in this endeavour. We had to convince the general public and the responsible people in governments that the concerns were real and were well-founded.

In the modern environmental movements, scientific credibility all too frequently takes second place to political perceptions as the basis and rationale for priorities and action. The present task is to convince the public, the responsible people in governments, and particularly those scientists whose interests include virology, immunology, and epidemiology, that this is not just another doomsday scenario, and that it deserves immediate, serious attention. The fate of the two species, which traditionally have disposed of animal carcasses throughout the Indian subcontinent and which have had a unique religious significance, is only the first of the concerns. Contact of the white-backed and long-billed vultures with wintering birds of other species of the genus Gyps could facilitate the spread of a disease in vultures of the Middle East, Africa, and Europe. But also, in an era in which viruses and other disease factors have been shown to be potentially transmissible to humans from wildlife sources, any appearance of any suspected disease factor in any species should routinely be investigated as a potential public health hazard.

For reasons of time and space, and to facilitate communication, scientific references are not generally cited in this report. All statements, however, with the exception of personal communications, can be supported by the scientific literature. Data on the vultures in the Keoladeo National Park cited in this report are from: Prakash, V., Status of Vultures in Keoladeo National Park, Bharatpur, Rajasthan with Special Reference to the Population Crash in Gyps Species, J. Bombay Natural History Society (in the press), or are personal communications from Dr. Prakash.

Any additional information that would change, otherwise modify, or support the conclusions presented here would be very welcome.

Introduction

The situation in India of the white-backed vulture, Gyps bengalensis, and the long-billed vulture, Gyps indicus, must now be regarded as critical; extinction of either or both species, which were common throughout India until as recently as only three years ago, appears to be a possibility unless the factor(s) responsible for their population decline, which now exceeds 95% in at least some portions of their range, can be identified and corrected.

A pattern of unusual mortality of white-backed vultures was first observed by Dr. Vibhu Prakash of the Bombay Natural History Society in the Keoladeo National Park during the 1996-97 nesting season. Birds dropped dead from their roosts, died on their perches and remained suspended in the branches, or died on the nests; fledglings also were found dead in the nests. Approximately forty mortalities were recorded by the end of the nesting season in May 1997. Deliberate or incidental poisoning of the large-animal carcasses upon which the species feeds appeared to be the only plausible cause. A new disease factor appeared unlikely at that time; only about 10% of the vultures inhabiting the Park were affected over the course of the nesting season. A disease, or so it appeared at the time, would be expected to affect more birds within a shorter time period.

150 nests of the white-backed vultures were found in the Park during the 1996-97 nesting season, more than a 50% decrease from 353 nests recorded in 1987-88. It appears therefore that a population decline was already underway in 1996-97. Only 25 nests were found the following season in 1997-98. In 1998 it became apparent that populations not only of this species but also of the long-billed vulture were in rapid decline throughout all of India. A ‘Vulture Alert’ was issued by Dr. Asad Rahmani, Director of the Bombay Natural History Society, in November 1998, followed by a second in July 1999. A workshop was convened by the Society in Mumbai in August; participants confirmed both the magnitude and the extent of the decline of both species over large areas of India.

Current Status of the Two Species in Keoladeo National Park

Since the long-billed vulture nests on cliffs, it does not breed in the Park; the nearest nesting colony has been 50 km to the southwest. In 1998-99, the maximum count in the Park was 25 birds, a 97% reduction from a count of 816 birds in 1985-86. Since the ending of the last monsoon in September, 1999, only one long-billed vulture has been observed in the Park.

In 1998-99 the number of nests of the white-backed vulture declined further to 20 nests. During the present 1999-2000 season there were no nests in the Park until one was found under construction in late December. Only two other nests have been located in the vicinity of the Park. One of these produced a fledgling in 1998-99; on December 2. 1999, only one bird was observed at this site; it flushed from the nest, suggesting that it was alone and that there was no egg in the nest.

A small colony of white-backed vultures containing eight nests was located in late 1999 immediately adjacent to the village of Bangro in the higher country 66 km southwest of the Park. Two dead adults, however, were suspended in the branches of the trees, indicating that the mortality process observed at Keoladeo over the past three years was underway at this site. On 1 December, a sheep carcass was placed in the corner of a field; on 5 December, 11 white-backed vultures and 6 long-billed vultures were in the vicinity. One of the white-backeds displayed the drooping head syndrome (below) characteristic of sick birds.

Villagers reported a group of about forty birds feeding on a buffalo carcass some kilometers away. If the pattern observed at Bharatpur prevails, all or almost all of these birds can be expected to die over the next year. There is no basis for an optimistic assumption that these are ‘healthy’ birds that will constitute a nucleus of a recovering population.

On December 6, nine white-backed vultures including one juvenile were in the vicinity of the second nest that has been located just outside the Park. Efforts to trap birds for observations in captivity and to radio-tag others were shifted to this site from the village of Bangro. Under the direction of Peter Bloom, working in the collaborative program between the Bombay Natural History Society and the Office of International Affairs of the U.S. Fish and Wildlife Service, pit traps were dug in which a person patiently awaits the arrival of the target bird attracted to a carcass strategically placed within grabbing distance of the person in the pit. This technique was successfully used by Mr. Bloom to capture the last of the California condors in the wild, but only after many days of patient waiting. As of 31 December 1999, no vultures had yet been trapped but capture of several of those still present in the vicinity of Keoladeo appears only to be a matter of spending the sufficient number of hours waiting in the pit traps.

Symptoms Preceding Death; Reproductive Failures

On five occasions a white-backed vulture was observed by Dr. Prakash to be either sick or impaired over periods of about 32 days. Typically, they appeared to be drowsy; the neck would fall limp and hang. After appearing to wake up, the bird would raise its head, but then let it fall again. In each case the bird fell from the tree and died. During the period of illness, however, the birds could fly short distances and even feed their young.

In 1997-98 (25 active nests) and 1998-99 (20 active nests) no young were produced in the Park. Causes of failure were, respectively: failure to lay eggs, 20 and 60%; failure of eggs to hatch, 20 and 10%; death of young, 60 and 30%. Each of these causes of failure could be attributed to a deficiency of fitness in the breeding birds. Typically, a failure to breed is a result of food shortage, not a factor in the present case. Failure of eggs to hatch has largely been, with egg breakage, a result of eggshell structural abnormalities caused by DDE, a derivative of the pesticide DDT. Imperfect incubation behavior, however, is also a plausible cause of failure of these eggs to hatch. Death of young in the nest is usually, like a failure to breed, a consequence of food shortage. The most plausible interpretation of these observations is that all of the birds were impaired, even those that showed no symptoms of sickness.

Such a pattern of reproductive failure has not been observed in any of the many studies undertaken on the effects of environmental contaminants on birds, including the many studies of birds of prey.

Preliminary Autopsy Results

To date, three autopsies have been performed, two by the Indian Wildlife Health Co-operative at the College of Veterinary Sciences, Chaudhary Charan Singh Haryana Agricultural University in Hisar. The first bird was recovered after falling into the water at Keoladeo in October 1999. The most striking symptoms of illness were in the kidney: “Degenerative changes in the urinary tubules in the form of deep eosinophilic epithelial cells, many of them lost their nuclei (early stages of necrosis). Presence of urate tophi in the glomeruli were well evident as radiating eosinophilic masses. Mononuclear cell infiltration around the glomeruli in the interstitium particularly lymphocytes and monocytes.” “Whitish deposits" assumed to be urates were present on the abdominal visceral organs including the heart, liver, kidney and spleen (quotations from the autopsy report of Drs. Gaya Prasad and S.K. Mishra).

No evidence of bacterial infection was found; samples of kidney, lung, liver, heart and intestine were cultivated in chicken embryo fibroblast primary cell culture and baby hamster kidney cell lines in an effort to detect viruses. As of 8 December, no definitive results were available. The bird had abundant fat in the abdominal cavity.

The second bird was found dead in New Delhi by Ms. Erika Wilson on December 6. It had been a member of one of the several pairs nesting in the vicinity of her house on Prithviraj Road. It was picked up on the following day by Dr. Prakash and myself and taken to Hisar for autopsy. The presence of several brownish wing coverts indicated that the bird was not quite mature, most likely four years old, breeding for the first time. Like the first bird, it had a large accumulation of fat in the body cavity and externally appeared to be healthy.

As in the first bird, the liver was whitish, with abundant accumulations of what we assumed to be crystals of uric acid. The condition is therefore similar to that of gout in people, which results from the accumulation of uric acid. If any analogy with the human situation is valid, the lethargic condition of sick vultures might be attributed to a reluctance to move.

The third autopsy was reported in the press, a summary of which was distributed by e-mail by Dr. S. M. Satheesen on 24 December 1999. The article had appeared in the Tribune of 22 December with the title “Vulture's death due to gout “ and was written by, or distributed by Ruchika Mohindra of Ludhiana. The death of a White-backed vulture in Harike Pattan on December 10 was attributed to gout on the basis of a postmortem examination carried out by the Department of Veterinary Pathology of Punjab Agricultural University; there was a “large scale deposition of uric acid crystals in the heart, kidneys, intestines and lungs of the bird which ultimately lead to its death.”

The progressive accumulation of uric acid may therefore be the cause of the impairment of reproduction observed in the Park during the last two seasons and the chronic condition that eventually results in death. The veterinarians consulted to date, however, have pointed out that the accumulation of uric acid crystals could be a secondary effect of either a slow-acting toxin or a disease factor. Professor Gerhard Verdoorn of the Poison Working Group and the Vulture Study Group of the Endangered Wildlife Trust of South Africa observed identical symptoms in 1995 in two young rehabilitated Cape Griffons. “They fell ill, heads drooping, lost appetite and died very shortly after symptoms set in... We saw the white crystal like nodes on liver, lungs and pericardium.” The condition was attributed to infection by the bacterium Klebsiella.

The appearance of what appear to be identical symptoms in vultures from three different areas of India strengthen a working assumption that the widespread population decline has a common cause.

The Possible Causes: Speculation and Hypotheses

Poisoned carcasses: Administration of a poison to cattle in order to harvest the hides, and subsequent consumption of the carcasses by vultures, was initially considered as a possible cause of the mortalities. Locally, the rodenticide zinc phosphide is known to have been used for this purpose. Such a practice could account for the deaths of about 10% of a local population, but could not plausibly account for a major population decline over much of India. Anticipated deaths of companion scavengers, particularly of village dogs, have not been observed.

Carcasses have sporadically been poisoned throughout India to kill jackals, hyenas, wolves, leopards and tigers; invariably vultures are also killed. But these are considered to be relatively rare events and are unknown in the vicinity of Keoladeo National Park, at least in recent times. Invariably, the poisons used for this purpose are acutely toxic which would either kill the birds within a short time period, or at lower, sub-lethal doses would induce sickness followed by recovery. Unless reinforced and enhanced through repeated exposures, induction of a chronic condition that becomes worse over time, invariably resulting in death, is not the expected pattern.

Collisions with any large bird continue to be a major hazard for aircraft; consideration of all of the possible causes of the vulture population declines must include the possibility that the Indian Air Force and/or other aviation interests have encouraged a directed poisoning campaign, perhaps at the slaughter houses that traditionally have attracted large numbers of vultures. Only a very slow-acting poison would explain the observed patterns of mortalities and reproductive failures; a suggestion on what this might be has yet to be made. In the absence of any supporting information, this hypothesis is not given serious credence.

Food Shortage: This is not a factor in the Keoladeo Park; many carcasses have remained unconsumed. Elsewhere in India carcasses traditionally consumed by vultures remain in a decaying state, becoming public health hazards.

Relocation and modernization of slaughter houses is reducing over the longer term the food supply available to vultures; populations will inevitably decline in response to a decrease in the food supply, but not sharply over a short period of 3-5 years.

Other factors are affecting the long-term food supply available to vultures. Bishnu Mahato, a naturalist working at the Gaida Wildlife Camp in the Royal Chitwan National Park in Nepal, has pointed out that while people have traditionally kept a large number of cattle in Nepal, many are now keeping buffaloes instead. Cows, sacred to the Hindus of Nepal, are never killed; when they die, carcasses are left for vultures. Buffaloes also produce milk, but are slaughtered for meat before they succumb to old age. A similar trend in Rajasthan has been reported by Mr. Harsh Vardhan.

This longer-term trend also can not account for a severe population decline over a three-five year period, nor the abundance of fat deposits in birds found dead.

A Pesticide Effect: Among the many documented effects of pesticides on non-target species, none are similar to those observed in the vultures. The more toxic of the pesticides to birds, including dieldrin and endrin among the organochlorines, monocrotophos and parathion among the organophosphates, and carbofuran among the carbamates, kill birds within a short time, or at lower doses produce sublethal effects from which the birds eventually recover. Moreover, if a pesticide use is responsible, the usage pattern must both have been new even if the pesticide itself was not, and it must have been introduced within a short time frame all over India. A new type of pesticide use, for example, might have been application of an organophosphate pesticide to the skins of cattle to control warble flies; such usage has killed birds of prey in North America. But there is no evidence that such a new usage has been introduced on a sufficiently wide scale to produce the observed effects. Mr. Harsh Vardhan has contacted the Director of Animal Husbandry for Rajasthan State in Jaipur on this point and was informed that such usage was minimal in Rajasthan.

The use of aldrin, which converts to dieldrin in the environment, was ended in India as of January 1994 by the Registration Committee established by the Indian Insecticide Act of 1968. Poisoning of Sarus cranes by dieldrin occurred in the vicinity of Keoladeo in the late 1980s. The extent of continuing use is unknown, but in any case its use would have been declining at the peak of the population collapse. Monocrotophos, a highly toxic organophosphate which is manufactured in India, has killed large numbers of birds and other wildlife in many countries, including India. But the observed mortality patterns are not consistent with the actions of any highly toxic insecticide.

A review of the environmental distribution in India of the persistent pesticides is the subject of a separate, fully-referenced, report in preparation. To date, detailed studies of two widespread species that are potentially at risk, the resident peregrine falcons and the Pallas’ sea eagle, have not been undertaken. Other subspecies of the peregrine falcon in North America and Europe, and two species closely related to the sea eagle, the bald eagle in North America and the white-tailed eagles in the Baltic Sea, experienced major population declines during the ‘organochlorine era’. In each case there were two contributing factors: depressed productivity caused mainly by the effect of DDE on eggshells, and enhanced adult mortality caused primarily by dieldrin, but also by DDT and heptachlor. The peregrine falcons in India, however, are known to produce young and apparently have not experienced a population decline. There appears to be insufficient information (?) on the current status of the sea eagle, which no longer breeds in Keoladeo National Park.

Concentrations of DDT compounds at levels several times higher than those that would inhibit the reproduction of bald eagles have been recorded in an unhatched egg of a lesser fishing eagle, Ichthyophaga humilis, from Corbett National Park in studies undertaken by Rishad Naoroji and Leon Pereira; the analyses were completed in my laboratory in California. Reports are now in preparation. The sources of this DDT contamination in an area that would appear ‘pristine’ are assumed to be upstream; they remain to be located. Use of DDT in malarial programs would not account for contamination of this magnitude. The high levels of contamination are of particular concern since the population of this species in India is small, and there has been no reproduction in the Corbett area in recent years.

Higher mean temperatures in India than in Europe and North America may account in part for the apparent lower sensitivity of the resident peregrines to DDT and aldrin/dieldrin. An increase in temperature of 10 degrees results in a doubling of the rate of volatilization into the atmosphere. Much of the DDT applied in India would therefore not persist in the local food webs but would instead contribute to the contamination of distant marine food webs.

The only production figures for DDT in India that I have so far found are 14,000 tonnes/year (Singh et al., 1988, Bull. Environ. Contam. Toxicol. 40:696) and a capacity of 10,000 tonnes/year (from a newspaper article by Ranjit Dev Raj distributed by 2000 InterPress Service on 3 January 2000). These figures might be compared with an estimated peak use in the USA in the early 1960s of 35 thousand tonnes/year and in Mexico of 4 thousand tonnes. It would be important to confirm and to update these figures. On a use/area basis present usage in India appears to be of the same order of magnitude as that in the USA during the years of peak use and of environmental contamination. In his article Mr. Raj attributes the disappearance of vultures from the Keoladeo area to DDT. As noted above, however, the mortality and reproduction patterns are not consistent with the effects of DDT compounds documented elsewhere; in my opinion therefore DDT is not a factor in this case. The analysis of tissues of the vultures found dead, and of two eggs collected in late 1999 will, however, provide a preliminary determination of the levels of DDT contamination in vultures.

The new laboratory facilities at the Salim Ali Centre for Ornithology and Natural History in Coimbatore will be able to provide information on current levels of contamination in India to meet the concerns expressed by Mr. Raj in his article. Two factors mentioned by Mr. Raj are particularly troubling. Use of DDT in agriculture results in higher exposure to DDT of the mosquito vectors of malaria, increasing the rate at which they become resistant; the incidence of malaria then rises in the human population. Secondly, the uncontrolled use of pesticides inevitably results in local problems for wildlife, of which the fishing eagles in Corbett National Park appear to provide an example.

A New Environmental Chemical: The arguments against a new type of pesticide effect apply also to a new environmental chemical derived from a non-agricultural use. No evidence has been found to support the hypothesis.

A New Disease: A new-disease hypothesis would have to account for the apparent failure to infect the two other species of vultures that breed in Keoladeo National Park, the Egyptian vulture , Neophron percnopterus, and the king vulture, Sarcogyps calvus. Five nests of the Egyptian vultures were recorded in 1985-86, 86-87 and 87-88 with an average nesting success of 50%. In 1996-97, 97-98, and 98- 99, three pairs nested with a nesting success of 0, 0, and 70%, respectively. The number of king vulture nests over this period has ranged between 2 and five, with no evidence of a downward trend or a decline in nesting success. Interspecific and intergeneric differences in susceptibility are a possible reason, but both of these species are either solitary feeders on smaller carcasses, or feed in small groups. Transmission of a disease factor from one bird to another might more readily occur in the crowded groups of Gyps vultures that typically feed on larger carcasses. Consumption of food regurgitated by another vulture is also a possible mode of transmission. The continued health of the other two species does not therefore weaken the hypothesis that a disease factor is affecting the white-backed and long-billed vultures. The status, however, of the Eurasian griffon, Gyps fulvus, in India is of concern. It is a winter visitor to the park; numbers have declined sharply in recent years.

Typically, viruses do not kill all members of their host species. Mutants that are more virulent may kill many individuals but the immune system induced by the more benign parent strain is usually able to protect the remainder. This pattern, however, can not be expected if the disease agent, presumably a virus, came from another species and is appearing in vultures for the first time. In this case the only hope for survival of either species might be isolation of a few uninfected individuals in remote areas (or in zoos). If, however, reservoirs develop in other species even these vultures might not be immune. A report by villagers to Dr. Prakash that they had found dead crows is not reassuring. Crows frequently are the first birds to appear at carcasses later consumed by vultures. Death of large number of crows near Aligarh, about 80 km from Bharatpur, has been reported by Mr. Pratap Singh; in this case pesticide poisoning may have been the cause of the mortalities, but careful attention might now be paid to any reports of deaths of crows or of any other species that feed on carcasses.

A new-virus hypothesis, probably a virus acquired from another species, or another new-disease factor, appears therefore to be the most plausible among the several hypotheses that have been proposed to account for the deaths of vultures and of their population decline. It is consistent with the sickness and mortality pattern observed, and no observations or findings have so far been made that would weaken or dismiss it. Our earlier conclusion during the nesting season of 1996-97 that a disease factor was unlikely was based on the assumption that a disease would affect more birds in a shorter period of time. Subsequent observations, however, are consistent with a disease factor that has a very long incubation period.

Priorities: URGENT

The only defensible response at this time would be to send tissue samples of sick or dead vultures to whatever laboratory in the world that has the capability of identifying and characterizing a disease factor and that is willing to undertake the work. Dr. Rahmani of BNHS and Dr. A.M. Bhagwat of the C.B. Patel Institute in Mumbai have suggested that the initial approaches be made to the National Institute of Virology in Pune.

Success would more certainly be achieved if several laboratories, each using its own techniques and approaches, were to participate in this project. The programs that determined the cause of the disappearance of the peregrine falcon in eastern North America and of their population declines elsewhere were multi-institutional and international. The recent identification and characterization of the AIDS virus, now believed to have entered the human population from monkeys or chimpanzees, was a multi-institutional, international effort. Moreover, spread of the hypothetical disease factor to other Gyps species in the Himalayas, the Middle East, Europe, and Africa must be anticipated, if it has not already occurred. An international effort is therefore justified. But because the problem at present is primarily an Indian concern, the means might be found for Indian scientists to visit and to work in participating laboratories outside of India in order to increase the expertise that will be essential in longer-term programs.

Priorities: Other

If a virus or other disease factor is identified, the evident priority is to determine its origin. Did it ‘jump’ from another species? And might it ‘jump’ to others? As noted above, it would be important to look for the disease factor in other species that also feed on carcasses, particularly crows.

Within India, public health authorities might be informed of the probable presence of a new disease factor in the environment, compounding the threat to public health resulting from the presence of unconsumed carcasses in the immediate vicinity of villages. Although the possibility of transmission to humans might be remote, the appearance of any suspected disease factor in any species should now be considered a potential hazard to human health; identification and characterization should be considered a routine response.

What appears to be an extinction process affecting the two species breeding in peninsular India may also be affecting both the Himalayan Griffon, Gyps himalayensis, an uncommon winter migrant to the Park last observed in 1996-97, and the Indian (or Eurasian) Griffon, which is as noted above a winter visitor that has declined sharply in numbers in recent years. Moreover, a disease would most likely eventually spread to the Gyps vultures of the Middle East, Europe, and Africa. A census of all potentially affected populations is therefore called for, with particular attention paid to any symptoms suggesting the presence of the disease vector observed in India. The monitoring of breeding success, which might be the most sensitive indication of infection, should be initiated, or continued if already underway.

Within India, it is very important that detailed observations be made of surviving colonies such as those in the village of Bangro, and the group Ms. Wilson is watching in New Delhi. Any studies of nest success, home-range size, feeding areas, etc. would be useful. Hopefully, individuals will be found that are resistant to the disease.

It would appear to be important to inventory the two species now in zoos throughout India and the rest of the world. Is this population sufficiently large to constitute a captive breeding population? It is particularly important that these birds not be exposed to any that have recently been brought from the wild, lest they acquire a disease factor now present in the wild population. The zoo-keepers might be asked whether there been any recent abnormally high mortalities of Gyps vultures within zoos in India, or mortalities of other birds. Some zoos (Calcutta) have open air facilities with resident wild Gyps. Any birds now in captivity and apparently healthy should be regarded as priceless.

Although contaminants to not appear to be contributing to the population declines, it is nevertheless important to analyze all available tissues for the organic contaminants that can be detected and identified and for heavy metals. I am planning to return to India in April to participate in such a program, in the laboratories of Dr. S. Muralidharan at the Salim Ali Centre for Ornithology and Natural History in Coimbatore and of Dr. A.M. Bhagwat at the C.B. Patel Institute in Mumbai. All available vulture tissues and eggs would be analyzed at that time.