A program to save South Asia’s wild vultures from extinction by breeding captive populations may be an exercise in futility, according to research released today.
Captive colonies are too small to protect the species from extinction, University of Michigan scientists have determined.
Vultures once numbered tens of millions in India, Nepal, and Pakistan, where they provided valuable health services by consuming the remains of animal carcasses quickly. The birds also disposed of human remains set out for them on sacrificial “towers of silence” by adherents of the ancient Parsi religion.
When numbers of the bird crashed to a few thousand across the entire subcontinent the impact was dramatic. Rotting carcasses stunk up the countryside, incubating disease. Populations of feral dogs scavenging on the meat bonanza exploded, and the dogs also spread diseases, including rabies.
Parsis, whose religion prohibits burying or burning their dead, had to resort to technology such as solar reflectors to hasten decomposition of corpses.
The fate of South Asia’s vultures is a tragic story. When their numbers began to plummet in the mid-1990s researchers were mystified. By the time the cause was identified–widespread use of diclofenac, a non-steroidal anti-inflammatory drug that had become a popular treatment for ailing livestock–several vulture species were on the brink of extirpation.
Diclofenac is readily substituted with a drug that is non-lethal to vultures. Regional governments banned its manufacture in 2006. But the drug continues to be available–so vultures continue to die.
Populations of the Asian white-backed vulture (Gyps bengalensis), long-billed vulture (Gyps indicus), and slender-billed vulture (Gyps tenuirostris) had declined by more than 95 percent in Pakistan, India, and Nepal, National Geographic News reported in May 2004.
Several species of Asian vulture will be extinct within a decade, National Geographic News contributor Dan Morrison reported four months ago. “A survey of vultures in northern and central India has found the birds’ populations have plunged to near-extinction levels–one species is down 99.9 percent since surveys began in the 1990s,” Morrison reported.
In our 2004 story, contributing editor John Roach reported that 20 to 30 years of captivity was thought to be the only option left to save the south Asian vultures from extinction. His story focused on a concept envisioned by conservationists is to place 25 breeding pairs of each of the three most threatened vulture species in at least three different facilities and encourage the birds to breed and raise young.
“Once the environment is cleaned of diclofenac, the young vultures will be released back into the wild. There, they will establish a viable and sustainable population, conservationists hope,” Roach wrote.
The Peregrine Fund successfully used this technique to rescue the peregrine falcon (Falco peregrinus) from extinction in the 1970s. Also, the fund is currently using it to help save the Aplomodo falcon (Falco femoralis) and the California condor (Gymnogyps californianus).
But the latest research, published online August 15 in the journal Biological Conservation, suggests the program is not working.
Adding wild birds to the captive colonies, located in Pakistan and India, is crucial, but political and logistical barriers are hampering efforts, says lead author Jeff A. Johnson.
When any large population crashes, as the vultures have, the amount of genetic diversity in the population also is likely to dwindle, Johnson says. “This is a concern,” he explained, “because a population’s genetic diversity reflects its ability to adapt to environmental challenges such as changing climate or outbreaks of disease. Without the ability to adapt, populations and whole species may become extinct.”
Johnson and coworkers used museum specimens collected before the decline began, along with recent feather and tissue samples from birds in Pakistan’s last remaining wild breeding colony, to see how genetic diversity in the wild population has changed as the population has plummeted. Then, assuming captive populations of various sizes, they used computer simulations to determine how large captive populations must be to preserve genetic diversity, the researchers said in a news release.
“The analysis showed that while there was still a fair amount of genetic diversity in the wild population two years ago when their last samples were obtained, current captive populations are not large enough to maintain that diversity if the wild populations are wiped out–a fate that seems inevitable if people keep using diclofenac.”
The simulation results also suggest that levels of genetic diversity in the wild may already be in decline.
“We know the problem, and we know the solution,” said Johnson, who was an assistant research scientist at U-M when the research was done and recently accepted a position as an assistant professor at the University of North Texas in Denton. “We just need to get diclofenac out of the environment and more birds into protection before it is too late.”
“One of my goals with this paper,” Johnson said, “is to raise awareness of the problem and to increase political will in India and Pakistan to get this matter resolved.”
Johnson’s coauthors on the Biological Conservation paper were Martin Gilbert of the Wildlife Conservation Society, Munir Virani and Muhammad Asim of the Peregrine Fund, and former U-M professor of ecology and evolutionary biology David Mindell, now at the California Academy of Sciences. The researchers received funding from The Peregrine Fund.
Photos taken in Pakistan by Munir Virani