In 1870 Sir Monier Monier-Williams, a prominent Sanskrit scholar at Oxford University, wrote a vivid description of the Towers of Silence, in Bombay—squat, drum-shaped structures where the Parsis of that city deposit their dead to be eaten by birds.
Though wholly destitute of ornament, and even of the simplest moulding, the parapet of each Tower possesses an extraordinary coping, which instantly attracts and fascinates the gaze. It is a coping formed, not of dead stone, but of living vultures. These birds, on the occasion of my visit, had settled themselves side by side in perfect order, and in a complete circle around the parapets of the Towers, with their heads pointed inwards, and so lazily did they sit there and so motionless was their whole mien that, except for their color, they might have been carved out of the stone-work.
According to Monier-Williams, it took the vultures less than five minutes to consume the flesh of a new corpse. The skeleton would eventually be added to a dry well at the towers' center, to mingle with those of other departed members of the community.
Visiting Bombay today, Monier-Williams would find a vastly different sight. Although the Parsis continue to stack their dead within the towers (their religion, Zoroastrianism, forbids them to contaminate earth, fire, or water with their corpses), the bodies remain unmolested except by the gradual effects of the elements. The vultures crucial to their rapid disposal have largely disappeared. The phenomenon has sparked an ongoing international scientific investigation; however, the reasons for the decline of the vulture population remain unclear. And it is estimated that 90 to 96 percent of India's vultures have already disappeared.
In the early 1990s the Parsis started to notice that there were fewer birds at the towers. At first they assumed that the vultures had simply gone elsewhere—even though large birds are unlikely to abandon a stable source of food. But researchers in other parts of India began to observe a similar condition. In 1997 Vibhu Prakash, a scientist at the Bombay Natural History Society, recorded about forty vulture deaths in a colony in Keoladeo National Park, south of New Delhi—nearly 700 miles from Bombay. Many of the vultures had exhibited a strange behavior before dying, hanging their heads so low that their beaks nearly touched their bellies. In November of 1998 the BNHS sent a "vulture alert" to its patrons and to various organizations around the world, including the U.S. Fish and Wildlife Service and The Peregrine Fund, both of which joined the investigation.
Initially, many scientists suspected pesticides, which have been implicated in the declines of several bird species in the United States, including the brown pelican, the bald eagle, and the peregrine falcon. But although India still uses vast quantities of DDT, the chief culprit in those species' decline, several facts argued against its having caused the vultures' deaths: DDT breaks down much more rapidly in warm climates than in moderate or cold ones; it tends to affect egg development rather than to kill adult birds; and tissue analysis of Indian vultures revealed only low levels of DDT metabolites.
In the spring of last year Robert Risebrough, a research ecologist who is retired from the University of California system and is now a consultant for the Fish and Wildlife Service, was checking pesticide levels in dead birds in India when he met up with Munir Virani, a Kenya-based raptor biologist who had been sent by The Peregrine Fund to evaluate the problem. Risebrough and Virani spent ten days in Keoladeo Park and nearby areas in the Indian state of Rajasthan, after which Virani visited West Bengal and the Himalayan floodplain in southern Nepal. Everything they saw confirmed the gravity of the situation. But they soon ran into an obstacle. India, fearing the loss of genetic material to pharmaceutical companies and other organizations interested in patenting the genomes of various organisms, forbids the export of tissue for analysis. In June of last year The Peregrine Fund therefore decided to extend its efforts to Nepal and also to Pakistan, where vulture populations were diminishing and many of the birds, especially near the Indian border, were exhibiting the same strange head drooping.