The funeral rites of the Parsis people of India rely a good deal on vultures.

The Parsis, who are Zoroastrians, believe that the elements earth, fire and water are sacred. They must not be contaminated with the dead. Bodies cannot be buried, burned or committed to the deep.

So the Parsis build structures they call Towers of Silence. They place their dead in them and vultures devour the flesh.

Such a ceremony might seem grotesque to Westerners, but it is an efficient way of disposing of corpses rapidly, which also protects public health.

Today, the Parsis face a spiritual crisis. The supply of bodies remains strong but they are running out of vultures.

According to BirdLife International, the white-rumped vulture was considered to be one of most common large birds of prey in the world, but by 1996 their numbers had crashed in their former strongholds. By mid-2000 the organization said that the birds "were being found dead and dying in Nepal, Pakistan and throughout India, and major declines and local extirpations were being reported".

In addition to inducing a crisis in one of the world's most ancient religions, the decline of the subcontinent's vultures nicely illustrates the law of unintended consequences. Vultures as scavengers dispose of a large amount of organic waste of all types. As the vulture population has declined in India, the population of feral dogs apparently has skyrocketed.

One researcher counted 60 dogs at an Indian dump in the early 1990s, competing with vultures for the goodies contained there. Following the vulture population crash late in the decade, the researcher counted 1,200 dogs at the same dump.

The loss of scavengers is just the beginning of a worldwide crisis in avian fauna.
"Our projections indicate that by 2100, up to 14 percent of all bird species may be extinct and that as many as one-out-of-four may be functionally extinct - that is, critically endangered or extinct in the wild," said Cagan H. Sekercioglu of the Stanford Center for Conservation Biology. "Important ecosystem processes, particularly decomposition, pollination and seed dispersal, will likely decline as a result."

Sekercioglu, a Turkish conservation researcher, published a paper in the December issue of the Proceedings of the National Academy of Sciences. It finds that 10 percent of all bird species are likely to disappear by the year 2100 and another 15 percent could be on the brink of extinction by then.

"The main purpose of my research was to find out which ecological functional groups of birds are more threatened than average," Sekercioglu told UPI's Blue Planet. "That's what I consider novel."

Sekercioglu collected more than 600,000 "data points" about 10,000 bird species. Then he divided them into functional groups: scavengers, fish-eaters, plant-eaters, fruit-eaters, omnivores, vertebrate-eaters (mostly birds of prey), invertebrate-eaters, seed-eaters and nectar-eaters.

"When we divided by functional group, we found that two-out-of-five scavenger species are extinction-prone," he said. "Thirty-four percent of fish-eaters are extinction-prone."

He found the nectar-eaters currently are least at risk but by 2100, he added, "they will be one of the most extinction-prone groups. A lot of them occur in a small area. In a small range the risk of extinction is higher."

The risks differ among groups. Research published in the British journal Nature last January found the Indian vultures are being wiped out by a drug called diclofenac, which is used on cattle. Diclofenac has also been used for a long time on humans. It is an anti-inflammatory used to control gout, for instance. The vultures ingest the drug from eating the carcasses of dead cattle.

Fish-eaters mostly are sea birds that get caught on hooks used in long-line fishing. They are also very long-lived and reproduce quite slowly, often with a clutch of only one or two young every few years, so their populations do not replenish as rapidly from these excess deaths.

On the other end of the spectrum Sekercioglu's research indicated seed-eating birds will probably prosper.

"We are losing all these bird functional groups that are providing valuable services, and increasing seed-eaters, which are major agricultural pests," he said.
The complexity of ecosystems virtually ensures the loss of even one bird species will have unexpected effects. The most famous extinction of an American bird was the loss of the passenger pigeon, which once numbered between 3 billion and 5 billion.

Passenger pigeons primarily ate acorns. One researcher has speculated that with the loss of this bird, the population of mice exploded as a result of the increased availability of the acorns. Mice are a reservoir for Lyme disease, so it may be that the loss of the passenger pigeon is indirectly responsible for Lyme disease becoming a public health issue.

Bird species declines are not confined to the misty past. The last captive Po'o-uli, a Hawaiian honeycreeper, died last week. The po'o-uli is the world's rarest bird. The last two individuals known in the wild have not been seen for a year.

The last pair of 'alala, the Hawaiian crow, disappeared in December 2003. The bird was declared extinct in the wild on November 17, 2004, although 40 'alala still reside in captive breeding centers in Hawaii.

In his 1897 book, Following the Equator, Mark Twain described the Parsis burial ritual. He closed with what could turn out to be its epitaph.

"We took a final sweep of the wonderful view of plain and city and ocean, and so ended our visit to the garden and the Towers of Silence," Twain wrote, "and the last thing I noticed was another symbol - a voluntary symbol this one; it was a vulture standing on the sawed-off top of a tall and slender and branchless palm in an open space in the ground; he was perfectly motionless, and looked like a piece of sculpture on a pillar. And he had a mortuary look, too, which was in keeping with the place."

Blue Planet is a weekly series examining the relationship of humans to the environment, by Dan Whipple, who covers environmental issues for UPI Science News