Has Mysterious Killer of India's Vultures Been Found?

John Roach
for National Geographic News
Updated May 4, 2004

When Lindsay Oaks went to Pakistan in the year 2000, there were so many vultures that he got bored looking at them. Now, three years later, the raptors are nearly gone. Within a few years, they may be extinct. The culprit appears to be a drug akin to aspirin and ibuprofen.

In a study that sheds light on a decade-old mystery, Oaks, a veterinary microbiologist at Washington State University in Pullman, and colleagues link the vulture deaths to the recent and widespread use of diclofenac, a non-steroidal anti-inflammatory drug that has become a popular treatment for ailing livestock throughout the Indian subcontinent.

Vultures, which once clouded the skies, were the subcontinent's carcass disposal system. When an animal dies, hide collectors remove the skin, leaving the rest for the birds.

But over the last decade, populations of the Oriental white-backed vulture (Gyps bengalensis), long-billed vulture (Gyps indicus), and slender-billed vulture (Gyps tenuirostris) have declined by more than 95 percent in Pakistan, India, and Nepal. Now, the carcasses rot for days, raising quite a stink throughout the region.

"Any time you have an animal die of disease and its carcass sits around, it's a problem," said Oaks. For example, in India, the rotting carrion supports booming populations of feral dogs, which in turn spread rabies.

Additionally, vultures play an integral part of the Parsi "sky burial" ceremony in which human corpses are left out to be consumed by the raptors. The lack of vultures in places like Mumbai (known earlier as Bombay) is causing significant problems for this ancient tradition, said Oaks.

Mystery Solved?

Until now, the cause of the vulture die-off has been a mystery. Theories ranged from the emergence of an unknown infectious disease to the buildup of pesticides in the vultures' tissues.

Based on an intense, three-year study of three rapidly declining Oriental white-backed vulture colonies in Pakistan, Oaks and his colleagues conclude that the vultures die after scavenging carcasses of livestock with diclofenac residues.

According to the study, which was posted today on the Web site of the science journal Nature, 85 percent of the 259 vultures tested died from visceral gout, a condition in which pasty, chalky white deposits of uric acid coat the internal organs. It is caused by kidney—or renal—failure.

In healthy birds, uric acid is excreted by the kidneys and is seen as the white material in their droppings. When the kidneys fail, uric acid builds up in the bloodstream and crystallizes on organs, especially the heart, liver, and kidneys.

The researchers performed tests to see if viral or bacterial infectious disease, pesticides, poison, heavy metals, or nutritional deficiency could explain the renal failure observed in dead vultures but found no such evidence. Instead, they found a correlation between kidney failure and diclofenac.

Continued on Next Page >>


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