India's vulture population crash actually began a decade ago. The results are now particularly evident in the north, around Delhi and in Uttar Pradesh and Rajasthan. One species in particular, the common white-backed Gyps bengalensis, has been virtually wiped out in some areas. A 1999 study by the Bombay Natural History Society (BNHS) found that the number of white-backed and long-billed vultures in Rajasthan's Keoladeo National Park, a world-famous bird sanctuary, had dropped by more than 95% in a decade. Nesting pairs dropped from 363 in 1987-88 to 20 in 1998-99, according to BNHS ornithologist Vibhu Prakash. In areas where vultures remain, many show signs of illness, such as prolonged periods of neck drooping. Such symptoms always seem to be fatal, according to Andrew A. Cunningham, a veterinary pathologist at the Zoological Society of London.

Cunningham says this may be the biggest die-off ever to hit these hardy birds anywhere. As creatures that live by scavenging, they are normally highly resistant to disease, and group mortalities are usually the result of pesticide poisoning. But Cunningham, who recently spent several weeks in India investigating the vulture die-off, says that an infectious disease appears to be the culprit. "An epidemic has not yet been confirmed," he says, but it's beginning to look as though "a viral disease is involved." It may take a while to isolate the cause, however. Vultures are normally loaded with pathogens, says Cunningham, so scientists will have to examine a lot of fresh carcasses to home in on the guilty party.