Catastrophic Vulture Die Off Creates a Stink in India
By Pallava Bagla, National Geographic News, November 14, 2000
The stench is overpowering. Rotting cattle carcasses seem to be strewn all over northern India now that nature's highly efficient clean-up brigade - vultures - are dying off in catastrophic numbers. Such a large-scale die off of this hardy group of scavenger birds is believed to be unprecedented in the world. Over the past decade in India, entire populations of vultures have declined catastrophically. In some areas they have been wiped out. A 1999 study by the Bombay Natural History Society (BNHS), in Keoladeo National Park, found a 96 percent decline in the population of white-backed vultures and a 97 percent drop in the population of long-billed vultures. According to Vibhu Prakash, an ornithologist with the BNHS, the nesting population of white-backed vultures within this protected area has crashed 95 percent over the last decade. During the 1987-88 season 363 nesting pairs were counted in the park. That number dropped to a mere 20 in 1998-99. "The vulture die off has created a real vacuum in the ecosystem," says Shruti Sharma, director of Keoladeo National Park. Without the vultures to scavenge dead animals, "rotting carcasses lie around for days."
In areas where vultures remain, many show signs of a mysterious illness that is characterized by prolonged periods of neck drooping. Adults, juveniles, and nestlings are all being affected by the disease, and invariably die as a result. Typically, die offs follow toxic exposures, leading scientists to believed the current situation may be linked to the use of pesticides. But new investigations have shown that a more likely cause of the decline is infectious disease. This is unusual, as vultures are highly efficient scavengers and are normally resistant to many diseases due to the scavenging nature of their lives. "An epidemic has not yet been confirmed, but the more progress we make with our investigations, the more likely it seems that a viral disease is involved," says Andrew A. Cunningham, a veterinary pathologist at the Zoological Society of London, who recently spent several weeks in India investigating the situation. Cunningham speculates that a "scenario of the introduction of a pathogen into native populations may have occurred." He feels there are strong similarities between the vultures in India and recent amphibian die offs in Central America and Australia that have been attributed to "pathogen pollution." Symptoms of the disease have also appeared in birds in Nepal and Pakistan, indicating the epidemic is spreading.