Too Few Asian Vultures in Captivity to Save Species?

Kimberly Johnson
for National Geographic News

September 12, 2008

Captivity strategies aimed at protecting endangered giant vultures may not be enough to save the birds from extinction, according to a new study.

Genetic testing of captive oriental white-backed vultures suggests the diversity needed to ensure the species' future will taper within three years.

The findings highlight the immediate need to put more of the beleaguered vultures into captivity before it is too late, said Jeff Johnson, lead author of the research, published recently in the journal Biological Conservation.

Until recently the species was considered the most common raptor in the world and its habitat extended deep into South Asia.

The large scavenger birds still exist in the region, but their numbers have dropped significantly since the mid-1990s.

(Read more about threats to Asian vulture species.)

The oriental white-backed population was in the millions as recently as 15 years ago. Now there are fewer than ten thousand, said Johnson, who was an assistant research scientist at University of Michigan when the research was done and is now an assistant professor at the University of North Texas in Denton.

(Watch video about Pakistan's vultures.)

The plunge in population size is a direct result of the birds feeding off animal carcasses treated with the anti-inflammatory drug diclofenac.

(Related story: "Has Mysterious Killer of India's Vultures Been Found?" [Updated May 4, 2004])

The drug is toxic to the birds, killing them within two days, Johnson said. It has killed more than 95 percent of the oriental white-backed species, which is officially known as Gyps bengalensis.

"It's really scary," he said of the species' sharp decline. "It's not common for something like this to happen."

Protection Efforts

Today about a hundred of the vultures are in captivity, distributed among three major facilities in Pakistan and India, Johnson said.

The facilities, however, are separated due to political and logistical barriers that "potentially hamper exchange … and the maintenance of genetic diversity even further," the study said.

"There need to be more facilities to house these birds," Johnson said. Computer simulations suggest that at least 300 vultures would have to be in captivity to protect the diversity needed to ensure the species' ability to adapt to changing environments and recover.

The study was based on genetic diversity analysis of vulture breeding colonies in Pakistan from 2000 to 2006.

The last survey samples were taken in 2006, however, so the diversity levels could already be in decline, Johnson said.

(Related story: "Can Captive Breeding Rescue Vultures from Extinction?" [May 11, 2004])

Bad Drugs

Key to the species' long-term recovery is the removal of diclofenac from the vulture's habitat.

Researchers were told that manufacturing of the drug has now been banned in the region, but Johnson was skeptical that the measure would be enough to keep diclofenac from showing up in the vulture's natural habitat.

"Certainly there's a stockpile of the drug left in India," he said.

Farmers in the area may also be giving their livestock a form of the drug that is approved for humans and not banned.

Todd Katzner, director of conservation and field research at the National Aviary in Pittsburgh, Pennsylvania, agreed with the study's dire message that as many oriental white-backed vultures as possible need to be put into captivity.

"The threat to these birds is immediate, and birds that are not brought in are almost certain to die," he said in an email.

However, there still is hope for the species.

"If diclofenac is removed completely from the environment, then it is possible that these populations will recover," Katzner said.

"It is generally assumed that these populations are unlikely to return to their former levels," he said. "But they could reach a new stable state, probably with fewer birds."