PUSHING open the cage door sends the tiny monkeys inside scrambling for cover. ``They have to be taught everything, even how to peel a banana and look behind leaves for bugs,'' says Mike Morgan, a spokesman for the National Zoo, which runs the sprawling research complex here devoted to breeding and studying rare animals.
These golden-lion tamarins - named for their lion-like plumes of orange hair - are being groomed for the South American jungle. The animals, which have never been outside a zoo in their lives, will eventually be flown to Brazil and released into the rain forest in which the species once thrived.
They're just one of several species being ``reintroduced'' to the wild in countries around the world. Others include the Arabian oryx in Oman, the P`ere David's deer in China, and an exotic bird called the Jalak Bali in Indonesia.
The rise of reintroduction programs underscores a fundamental shift in the way zoos do business. These programs are costly and controversial but hold the allure of putting depleted species back into nature.
In the past, when zoos needed to replace an animal, they could just buy another pulled from the wild. But as a growing number of species have become depleted in their native habitats, zoos have had to become skilled at breeding the animals themselves. New reproductive technologies and a greater understanding of the biology of exotic animals have been crucial to this development.
Today, animals living in different zoos are managed as though they were one large colony, with mates sometimes transferred thousands of miles so that the population maintains genetic diversity.
Reintroductions carry this trend toward close management of endangered species one step further, using well-established zoo populations to restock the wild. The golden-lion tamarin, for instance, now has a self-sustaining captive population of about 500 animals in 90 zoos worldwide.
Before being released into the wild, small groups of the squirrel-size primates are given survival training, such as being shown how to forage for food. At last count, two dozen captive-born animals were living in Brazilian jungle preserves closely monitored by scientists.
Typical ``training'' procedures include offering the animals a wider variety of foods and hiding food around the animals' cage, forcing them to search it out the way they would in the jungle. Cage interiors are designed to include plenty of unstable branches, bunches of leaves, and other details that condition the monkeys for moving around unfamiliar surroundings.
``After the first year, we realized that the animals were klutzy - they didn't know how to move through the trees,'' says Devra Kleiman, associate director for research at the National Zoo.
The animals even had to be coaxed to go out on narrow branches, she says, since most zoo interiors had large, stable branches.
``These sorts of programs can't be undertaken by a single institution - so they literally force cooperation,'' says Richard Block, director of public programs at the World Wildlife Fund.
Eleven United States zoos contributed to the reintroduction of the Jalak Balis in Indonesia, for example. The effort began when it was found that the wild population of the birds had dwindled to about 60, while zoos in North America had more than 500 and could readily breed more. The US zoos agreed to produce 40 surplus birds last year, which were sent to a zoo in Surabaja, Indonesia.
If all goes as planned, offspring from this breeding colony will be released into a national park on the island of Bali this spring.
``Captivity changes the behavior of animals,'' so you can't just dump them into the wild, says Chris Wemmer, head of the Conservation and Research Center in rural Virginia. The center, an agency of the Smithsonian Institution's National Zoological Park in Washington, is a vast laboratory for working with endangered species, only some of which are earmarked for reintroduction.
In a valley outside Dr. Wemmer's office, a herd of highly endangered P`ere David's deer gather behind a clump of trees to avoid the bitter January wind.
According to Wemmer, reintroductions have been attempted with at least 60 different vertebrates, ranging from the peregrine falcon to the musk ox.
As early as the 1890s, an American naturalist began releasing hand-reared snowy egrets into newly created habitat in the Mississippi Delta. And in Europe, a program to reintroduce captive-bred eagle owls has been under way since World War II.
But even advocates of reintroduction are quick to point out its limitations.
Only a tiny fraction of species can be saved through such programs. Often, the reason the animal disappeared in the first place makes reintroduction impractical. When wilderness is cleared for farmland, for instance, it may become impossible to find enough suitable habitat.
``These are also very costly programs, so you can't afford to do a lot of them,'' Wemmer says. The golden-lion tamarin program, for instance, costs more than $100,000 a year.
Some analysts worry about spending such large amounts on highly endangered species - some of which appear destined to become extinct no matter how hard scientists try to prevent it. The same money directed toward protecting habitats might accomplish more in the long run, some critics say.
Others question the ethics of tampering so heavily with wild animals. Many objected last year, for example, when biologists captured the last of the free-flying California condors. The birds were added to a breeding program that appears years away from putting any creatures back into the wild.
With the golden-lion tamarin, the first step toward reintroduction was figuring out how to keep the animal from going extinct in captivity. By the early 1970s, there were only about 70 animals in captivity and not many more than that living in fragments of jungle in Brazil.
Nobody was sure why the animals didn't breed well in captivity. Then researchers began experimenting with new ideas in managing the animals. They changed the animals' diet to match more closely what they eat in the wild and began allowing them to live in family groups, rather than the usual mixed breeding colonies.
As it turns out, the golden-lion tamarin is monogamous and thrives when allowed to live in family groups. One generation of children help their parents raise the next litter, thereby learning how to be good parents themselves. Now there are so many golden-lion tamarins being born that researchers are beginning to put on the brakes.
``We're still learning every day about these animals,'' says one researcher working on the project. Each new piece of information helps add to the picture, he says, and helps ensure the survival of the species.