Back to Nature

You can put a zoo-bred animal back into the wild. But that doesn't mean you're putting back anything like a wild animal.

By Peter RadetskyJul 1, 1993 5:00 AM


Sign up for our email newsletter for the latest science news

A small face pokes from between the branches of an oak tree. It has a thick golden mane and looks oddly familiar, like the cowardly lion in The Wizard of Oz. Soon it’s joined by another maned head, then two, three, four others. The animals are about the size of squirrels, with silky fur and dangling 12-inch tails. They scurry nimbly from branch to branch, 30 feet above the ground. Look at the monkeys, shouts a grade-schooler in a Washington Redskins cap, dribbling ice cream onto his T-shirt. Seemingly oblivious of the human crowd, the little creatures dart about the treetops, calling to one another with whistles and trills.

These golden lion tamarins are a long way from their ancestral rain forests in Brazil. But they are going back. They were bred here at the National Zoo in Washington, D.C., as part of a plan to rescue the endangered species and return it to its tropical habitat. In the meantime, to help them make the transition from the zoo cages where they were born to the wild that awaits them, they are living on a couple of wooded acres just down the path from the bison exhibit.

This tamarin equivalent of a halfway house was conceived by Ben Beck, a primatologist, and Devra Kleiman, the zoo’s assistant director of research, to address a vexing question in conservation biology: Once you’ve succeeded in breeding an endangered animal in captivity, how do you ensure that the animal will be fit to live in the wild? How much of its natural behavior will survive? The same worry underlies plans to return red wolves to Tennessee’s Great Smoky Mountains and to restore black-footed ferrets to Wyoming’s plains. For these efforts, the case of the golden lion tamarin is a prelude and an object lesson.

By the 1970s golden lion tamarins had almost vanished from Brazil, victims of their own appeal (the handsome animals were exported as pets) and of rampant deforestation. Hoping to reverse the trend, the Brazilian government set aside a 12,500-acre reserve in the rain forests north of Rio de Janeiro for some 100 wild survivors. In the United States, meanwhile, the National Zoo had become involved in breeding the animals in captivity. At the time, there were fewer than 80 golden lion tamarins in zoos around the world, and they were not doing well--deaths were exceeding births. Kleiman determined that one of their problems was diet. Zoos were feeding their tamarins traditional monkey fare: fruits and vegetables. But in the wild these animals also ate insects and birds’ eggs. When, on Kleiman’s recommendation, they were fed protein in the form of insect grubs, their health improved. Another problem, Kleiman found, was that because monkeys are usually social animals, zoos invariably caged tamarins in large groups. But if a group contained more than one adult female, Kleiman determined, only the dominant female gave birth. When tamarins were separated into breeding pairs, their birthrate shot up. By 1983 the worldwide zoo population of golden lion tamarins had risen to 370.

The following year, to bolster the wild population, Kleiman and Beck sent 13 tamarins back to the Brazilian reserve. They were in for a nasty surprise: the animals were almost helpless. We thought that their primary problem would be finding natural foods, says Beck. In fact it was more a case of not knowing what to do with food when they found it. Imagine a monkey that doesn’t know how to peel a banana, Beck says with a sigh.

But the tamarins’ main problem--which we failed totally to anticipate, says Beck--was their disorientation. They were lost in the rain forest. Raised in cages, they simply didn’t know how to plot a route through uncharted territory. Furthermore, they were used to climbing on sturdy lumber frames. Natural vegetation, which bent and swayed under their weight, literally floored them--they frequently fell. They preferred to crawl along the ground, a dangerous proposition for a small monkey. One fell prey to a snake, another to a feral dog. Seven others died or disappeared the first year--killed, perhaps, by such other predators as lizards and ocelots, or overcome by starvation, disease, and mishaps. We had to go back, regroup, and revise our techniques, says Beck.

A first experiment in tamarin jungle-training met with mixed results. At the National Zoo several cages were stuffed with natural, springy vegetation, forcing monkeys to negotiate their way over the plants to find their food. In 1985 Beck’s team released 11 tamarins in Brazil, 7 trained and 4 not. For the first couple of weeks the trained group clearly had an advantage, says Beck. They moved more easily in the trees and found more food. But the untrained group rapidly caught up, he adds. In fact, the survival rate was the same for both groups--very low. Only two of the animals survived beyond a year.

Still, it was apparent that the tamarins could learn, and might learn better given more appropriate conditions. That’s how the outdoor exhibit here at the zoo originated, Beck says. Since 1986 tamarin families have lived in the trees in the warm-weather months from May through October. (Insects and fruits, including bananas in their skins, are provided for them in the trees, not on the ground.) Those that take to arboreal living are then transported to the rain forest to tackle the real world. Not only do these animals do better, Beck has found, but their offspring, who receive the benefits of their elders’ experience, fare better still. As of this past January, Beck and his team had released 134 tamarins to the forest. Of those, 43 have survived. These 43 pioneers have given birth to 97 babies, of which 70 are still alive, for a grand total of 113 tamarins added to the existing wild population. Some 400 golden lion tamarins now roam the coastal forest of Brazil.

Curiously, says Beck, one thing that tamarins don’t forget in captivity is how to recognize their most common predators. Recognition of aerial predators is inborn, he says. Anything that flies over, any dark shadow, and they give an alarm call. Then they either drop to the ground or run right to the center of a tree to avoid them. This behavior is genetically hardwired--they don’t have to learn a thing about it. Tamarins are somewhat less wary of earthbound predators, perhaps because they can usually count on making a quick escape through the trees. Typically, when a tamarin encounters a threat such as a large snake, it approaches the animal noisily, as though alerting its family group to flee. (That first batch of disoriented, ground-hugging tamarins may have come to grief not because they failed to recognize their predators but because they failed to even detect them in time to make their clumsy getaway.)

Red wolves born in captivity don’t have to learn to recognize wild predators, either, but for quite different reasons. Nothing in the wild preys on a wolf. Nor do they need to learn how to find food.

They’ll readily hunt wild rodents, raccoons, rabbits, deer, even wild pigs. The problem with wolves is that they’ll also readily hunt livestock, chickens, and turkeys. If their reintroduction is to be successful, red wolves must adapt to the wilderness, not to the all-too- inviting civilization surrounding it. The key is instilling in the animals a sense of territory and fear of humans.

Red wolves have ample reason to fear humans. By the late 1970s these lanky canids (which once ranged halfway across the country, from Texas to North Carolina) had been driven from their ranges and slaughtered to near extinction. In 1987, however, a federal program to restore the species got under way with the release of some captive-born animals in North Carolina, at Alligator River National Wildlife Refuge. Then in November 1991 a family of four red wolves was introduced as an experiment to Tennessee’s Great Smoky Mountains National Park; for the first time in almost a century the howls of wolves were once more heard in the southern Appalachian mountains.

It was not a completely successful debut. Some of the animals weren’t sufficiently savvy or cautious--in short, they were not wild enough. A large male took three turkeys from a farm just outside the park, says Chris Lucash, the U.S. Fish and Wildlife biologist who runs the Smoky Mountain project. It wasn’t that big a deal. It’s not uncommon for a wild predator to take something like a domestic turkey. The problem was that the farmer came out and chased the wolf, but the wolf didn’t leave. He sat down in the woods just outside the garden and ate the bird. When the guy went to work, the wolf came back and took another turkey. By the time we got there he had taken still another one, despite the presence of people and a barking dog--that’s not a good wild animal. He had spent too much of his life in captivity. He was too comfortable with people. We recaptured him that day, and I didn’t turn him loose again. He was a liability.

As planned, Lucash ended his experiment after ten months and recaptured the rest of the family. He also rethought his strategy, having decided it was necessary to instill in the wolves a sense of territory and a wariness of humans. Now before red wolves taste freedom, they’re given an acclimation period in their own lupine halfway house. It consists of a pen 50 feet by 50 feet, with an 11-foot-high fence, set among the maple, oak, and pine trees of the Smoky Mountains. The wolves pass their first year there, amid the scents and seasonal shifts of the forest, mating and giving birth to pups.

Human contact is kept to a minimum. A caretaker who provides food and cleans the pen lives discreetly in a tent some 200 yards away. No visitors are allowed. Hikers or fishermen blundering into the area encounter a sign threatening a $20,000 fine for harassment of an endangered species. During most of 1992 two such pens on the western side of the park, separated by eight miles, provided transitional homes for two families of wolves, each consisting of an adult pair and their four pups.

The idea is to condition the animals to consider this plot their own. Food is plentiful in the Great Smokies, as is space--over 500,000 acres of it. If each group of wolves establishes a defined territory and sticks to it, not venturing into the ranches and farms bordering the park, one of the great hurdles facing the reintroduction will have been surmounted. Lucash envisions as many as eight family groups, possibly 50 animals, roaming the park, coexisting with one another, with farmers, and with the numerous visitors to the area.

Last October he took a step toward that goal by pulling open the gate to one of the pens. I put a pig carcass outside the pen so they wouldn’t just bolt out of the gate and run all over the place, says Lucash. A week and a half later I gave them another carcass, and three weeks later another one. That gave them time to hone their hunting skills and not starve.

Just as Lucash and his colleagues hoped, the wolves began to consider the pen the heart of their territory. They just hung out for the first week at the release area, says Lucash. Then they started going out into the meadow and regrouping at the pen. They left a lot of scent marks there, defining their territory. And they began to hunt. We saw them standing in a creek with a freshly killed 70-pound wild pig. We were pleasantly surprised by that.

In December Lucash opened the gate of the second pen. That meant 12 red wolves were now loose in country where just two years before there had been none. The strain began to show. Some of them have been acting a little stupid, says Lucash. We’ve seen them on the road. They’re not afraid enough of vehicles to satisfy me. I’ll probably have to do some negative reinforcement by shooting at them with exploding blank shells.

In January one of the pups released in December strayed out of the park into farm country; he was soon followed by his three siblings. Lucash and his crew returned the animals to the park, only to watch them stray again. The first pup wandered away three times. They weren’t necessarily misbehaving, says Lucash. It’s just that legally we can’t let them out of the park. They cross this imaginary line and they’re outlaws. Rather than perpetually retrieving them, Lucash decided to return the wandering pups to the pen.

That left eight wolves on the loose, and one of those has apparently made forays outside the park as well, judging from complaints Lucash has received about wolves taking chickens. I didn’t even argue with the farmer who reported them missing--a bus driver claims he saw a wolf with a chicken, says Lucash. I just paid the farmer for the birds.

Such behavior wouldn’t be too surprising in a not-quite-wild wolf. We knew that the problem we were going to have with these transitional animals was that they were still too accustomed to people, says Lucash. We can’t get around that until we get pups born and raised in the open forest. We’re just going to have to work real hard to get the animals through this transition until they start reproducing as real wild animals.

Wyoming Game and Fish Department veterinarian Tom Thorne agrees that keeping animals in a delineated area is the key to releasing them. Thorne is part of a joint venture between federal and state agencies to return black-footed ferrets to America’s plains. If they disperse to the four winds, they might as well be dead, he says. Even if they escape getting killed, their chances of finding a mate and contributing to a stable population are zero. We want to keep them at the release site for as long as possible, long enough so that they’ll consider it their territory and stick around. A tall order, as Thorne and his colleagues have found out, when you’re dealing with creatures as skittery, secretive, and nocturnal as ferrets.

These narrow, skinny two-pound animals are preyed on by coyotes, badgers, and owls, so it’s a matter of survival for them not to show themselves. They spend much of their time underground in prairie dog burrows, and prairie dogs constitute virtually their entire diet. Earlier this century you were likely to find black-footed ferrets wherever there were prairie dogs. But farmers destroyed vast networks of burrows by plowing, and the U.S. government (responding to ranchers, who regarded prairie dogs as pests) systematically exterminated them. Ferrets died from eating strychnine-poisoned prairie dogs, and as prairie dog towns dwindled, ferret populations became increasingly isolated and fragmented. In fact, black-footed ferrets were believed extinct until a group turned up in Wyoming in the early 1980s. Beginning in 1985, the last 18 of these animals were rounded up to start a captive-breeding program.

The current plan is to reintroduce the animals to Wyoming, then to Montana and South Dakota, and eventually to the entire West. But bringing them back isn’t proving easy. Just keeping track of the nocturnal animals is a challenge. Some are fitted with radio collars, but the collars are a burden to these small animals, and they are designed to disintegrate in about two or three weeks. After that biologists resort to spotlighting--sweeping lights across the prairie in the hope of glimpsing flashes of the ferrets’ emerald green eyes--and searching the wintry, snow- covered plains for small footprints before the wind erases them.

In addition, the animals’ vulnerability to predators has had biologists worried from the start. Had captivity blunted the ferrets’ wariness? Could you train them to avoid predators they had never seen? A ferret has one chance to learn about a predator: its first encounter, explains Thorne. It either lives or dies. And the difference between living and dying is getting into a burrow fast. In the late 1980s, with captive breeding of black-footed ferrets barely begun, biologists with the U.S. Fish and Wildlife Service in Front Royal, Virginia, were already thinking about ways to improve the animals’ chances. Using an unendangered ferret, the Siberian polecat, as a stand-in, they tried some rather fanciful experiments to gauge how well the animals would fare. A badger run over by a pickup truck in Wyoming was frozen and mailed to Virginia, explains Dean Biggins, who designed the experiment with fellow biologist Brian Miller (now at the National University of Mexico). The animal was stuffed by a taxidermist at the Smithsonian and mounted on a remote-control Radio Shack truck chassis.

Robo-badger, as he was called, was used to pursue captive-bred Siberian ferrets living in a pen riddled with burrows to provide escape hatches. To drive home the danger of the situation, the researchers fired rubber bands at the animals with a toy-store gun. For good measure they occasionally dive-bombed the animals with a stuffed owl slung from an ingenious network of pulleys. Even Miller’s Labrador, Rosa, was pressed into service, retrieving ferrets in her soft mouth before releasing them unharmed.

Still, when these animals were trucked into the wilderness of Colorado and Wyoming, they fared only somewhat better than those raised in cages. Though trained ferrets were more venturesome than untrained ones, they didn’t live any longer--the record was 34 days. It was sobering news, because wild ferrets live for two to three years.

Thorne’s team in Wyoming, meanwhile, has decided on a different tack. At the group’s ferret breeding facility north of Cheyenne, they’ve added a series of 22-by-20-foot outdoor pens, each enclosed by a chain link fence sunk 8 feet into the ground. When prairie dogs were released inside them, they quickly established miniature prairie dog towns. These training pens allow families of black-footed ferrets to live, hunt prairie dogs, and raise their young in wildernesslike conditions.

When it comes time to release the animals, they’re transported, barking and chattering, inside nest boxes to a windswept prairie called Shirley Basin, some 80 miles north of Laramie. There the team bolts the boxes to protective wire cages. Four-inch plastic tubing, big enough to accommodate a ferret but not a predator, provides safe passage from each cage to a nearby prairie dog burrow. After a ten-day acclimation period, a trapdoor springs open and the ferrets can wriggle along the tube to explore the surrounding plains and the labyrinthine tunnels beneath them. But they always have the security of the cage. If an owl swoops over them when they’re on the open plain, they can duck into the tube and back to safety.

It’s an offer they seem to refuse. Ferrets have been observed returning to the cages for no more than a few days after the trapdoor was opened. Just in case, the team keeps food and water inside them for five days past the last sighting, but by then the animals are long gone, fending for themselves in the prairie dog town and beyond--far beyond.

Last fall 90 captive-bred ferrets were set loose in Shirley Basin. To the biologists’ consternation, over half of them lit out for destinations unknown, for all intents and purposes lost forever. (They suffer from some sort of wanderlust, shrugs Biggins.) Of the 37 ferrets that were radio-collared, at least 10 are known to have been killed, mostly by coyotes. A hawk or eagle got one, says Biggins. We found wing prints and tracks in the snow. But at least 16 ferrets are still known to be alive on the site.

Those figures may look meager. But they’re better than those for 1991, the first year of the release program, when only 4 of 49 ferrets made it through the winter. In fact, the reintroduction team is quite encouraged. Those four original survivors gave birth to six kits, more than doubling their number. If the latest batch does as well, the black-footed ferret has a fighting chance of making a comeback. Thorne, for one, is looking on the bright side. Several days after the last release, he recalls with gratification, one of our guys saw ferrets near their cage in Shirley Basin. One was barking at him from a burrow right next door. He was sticking close to his territory, warning the human to get away--just as he was supposed to do.

1 free article left
Want More? Get unlimited access for as low as $1.99/month

Already a subscriber?

Register or Log In

1 free articleSubscribe
Discover Magazine Logo
Want more?

Keep reading for as low as $1.99!


Already a subscriber?

Register or Log In

More From Discover
Recommendations From Our Store
Shop Now
Stay Curious
Our List

Sign up for our weekly science updates.

To The Magazine

Save up to 70% off the cover price when you subscribe to Discover magazine.

Copyright © 2023 Kalmbach Media Co.