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Chapter in new ecotoxicology book details story of how Peregrine Fund experts found cause of Asian vulture die-off

BOISE, Idaho – Three years of painstaking research and field work in Pakistan paid off for Peregrine Fund researchers in 2003 when they proved that a veterinary drug called diclofenac was the cause of a massive and catastrophic die-off of vultures in Asia. 

Peregrine Fund Vice President Rick Watson and Washington State University veterinarian Lindsay Oaks tell the story of this landmark discovery in a new book, “Wildlife Ecotoxicology: Forensic Approaches,” published by Springer. The chapter they co-authored is one of several in the book that provide case-by-case examinations of how toxic chemical effects on wildlife have resulted in new policies and regulations aimed at improving the environment.

“Many people were working on this issue and we all experienced frustration and increasing alarm as vultures continued to die while we did grueling field work and an intensive diagnostic analysis,” Watson said. “Then came the moment of elation when we were able to prove conclusively that a pharmaceutical drug, recently introduced for use in domestic livestock, was the culprit.”

Within three years, India, Pakistan, and Nepal had banned the manufacture and sale of diclofenac. The drug has since been banned in Bangladesh as well.

“The initial response was remarkable because the national governments acted relatively swiftly to protect the vultures,” Watson said. “I wish this story had a happy ending, but unfortunately diclofenac is still being sold and used illegally. The story is far from over and the stakes are high.”

Diclofenac is an inexpensive anti-inflammatory drug used to treat ailing and dying cattle and other livestock. After animals die, they are left in the field to be eaten by scavengers, often with high enough levels of diclofenac remaining in their tissues to be toxic to vultures. After ingesting the drug, vultures die within days of kidney failure.

As a result, vulture populations that once numbered in the tens of millions dwindled to a few thousand in just a decade. Currently, three species are at risk of extinction and a fourth species appears to be in decline due to diclofenac.

Watson’s and Oaks’ detailed narrative takes readers on an environmental and scientific journey from uncovering the problem and identifying its cause, to presenting their case to regulatory authorities and getting a policy response. They also look at how the regulations have been implemented and their impact to date.

The authors recommended better law enforcement against the use, manufacture, or importation of diclofenac. They also recommended stepped-up efforts to increase awareness among veterinarians about an alternative, meloxicam, which is effective for livestock and safer for vultures. And a public education campaign would teach the public about the important niche that vultures fill in the environment, they wrote.

The book is dedicated to Oaks, who died in January 2011.

Copies of “Wildlife Ecotoxicology: Forensic Approaches” are available for sale and may be ordered from the publisher at:

Did you know?

  • The critically endangered Oriental White-backed Vulture (Gyps bengalensis) was one of the world’s most common birds of prey just 20 years ago. By the end of the 1990s, their numbers had declined by up to 99 percent. Recently, populations appear to be stabilizing.
  • Long-billed Vultures (Gyps indicus) and Slender-billed Vultures (Gyps tenuirostis) also are critically endangered due to the effects of diclofenac. Himalayan Vultures (Gyps himalayensis) are believed to be affected but are at a lower risk of extinction.
  • The Peregrine Fund established a project in 2000 to discover the cause of the catastrophic decline in abundance of these vultures, to monitor their population status, and maintain an online database for researchers and vulture enthusiasts to locate and monitor remaining vulture colonies.
  • The Peregrine Fund set up the first “vulture restaurant” in South Asia to provide diclofenac-free food for vultures.
  • In southern Asia, vultures fill important ecological and cultural roles. Because a flock of vultures can consume a carcass quickly, the birds help control the spread of infectious diseases. The void left by vultures now is being filled by dogs, rats and other animals more likely to come into contact with people.

For more information, contact:

Erin Katzner
Director of Global Engagement
Main Phone:     208-362-3716
Direct Phone:     208-362-8277