Back home on the range: biologists help black-footed ferrets come back from the brink of extinction.[ILLUSTRATION OMITTED]
On a cool summer night in Wyoming, Dean Biggins waits patiently in his truck. Every now and then he casts a spotlight across the surrounding grasslands. Suddenly, Biggins, a wildlife biologist who works for the U.S. Geological Survey, spots a pair of eyes in the distance.
Biggins can't believe his luck: He's just caught sight of a blackfooted ferret--one of the world's rarest animals.
Just over a century ago, hundreds of thousands of blackfooted ferrets roamed vast stretches of grasslands in North America known as the prairie. But the animals died off as their main source of food--prairie dogs--disappeared (see map, p. 18).
By the late 1970s, researchers thought black-footed ferrets were extinct. But they were wrong--and now, with the help of researchers like Biggins, these mammals are making a comeback.
Black-footed ferrets look similar to the ferrets that some people keep as pets, but the two are actually different species. Pet ferrets are a domesticated subspecies of Mustela putorius, which is native to Europe. Black-footed ferrets (Mustela nigripes) axe found only in North America.
The black-footed ferret's diet consists almost exclusively of prairie dogs another species that lives only in North America. Black-footed ferrets rely on prairie dogs for their shelter, too. After a ferret has eaten a prairie dog, it moves into the burrow where the prairie dog used to live (see Under the Prairie, below).
"Depending on prairie dogs for both food and shelter makes the ferrets very vulnerable," says Biggins. "Black-footed ferrets go the way of the prairie dog ... and prairie dogs haven't done that well."
When cattlemen started setting up ranches on the prairie in the early 1900s, they thought prairie dogs, which eat grass, might compete with their livestock for food. To make sure that didn't happen, they killed off billions of prairie dogs. These rodents once lived all over the prairie, which stretches from Canada to Mexico. Now, only a tiny fraction remains.
BACK FROM THE DEAD
As prairie-dog populations shrank, other animals that depended on them, besides blackfooted ferrets, also disappeared. Burrowing owls, a type of owl that also lives in empty prairie-dog burrows, faded away. So did mountain plovers. This bird relies on prairie dogs to nibble grass, creating clearings so plovers can build their nests on the ground. American badgers also suffered because there weren't as many prairie dogs to eat.
But black-footed ferrets were most affected. By 1979, researchers couldn't find any ferrets and declared the species extinct. Then, two years later, something amazing happened. A ranch dog left a mysterious dead animal on its owners' porch in Meeteetse, Wyoming. The animal had belonged to a tiny population of black-footed ferrets that was still thriving. Biggins and other wildlife biologists rushed to study the colony and try to save it.
Although scientists were excited about the newly discovered colony, it soon became clear that the ferrets were in danger. Fleas at the site carried sylvatic plague, a disease that was killing the ferrets and their prairie-dog prey. Soon, just 18 ferrets remained.
To help the species survive, the researchers took all the ferrets into captivity in 1986 and began breeding them, says Randy Matchett, a wildlife biologist at the U.S. Fish and Wildlife Service. Once the captive population was built up, researchers released some of the ferrets' offspring, or kits, into the wild.
MAKING A COMEBACK
Releasing captive-bred blackfooted ferrets onto the prairie is no easy task, says Matchett. When the ferrets were first released in Montana in 1994, nearly half died within two weeks. Because they had no experience living in the wild, they didn't know to find prairie-dog burrows to live in. They also didn't know how to avoid predators like hawks and coyotes.
To help the black-footed ferrets learn survival skills, wildlife biologists put them through a process called preconditioning. Researchers build a fence around old prairie-dog burrows and put the ferrets in when they are a couple of months old. While the animals get used to their new home, researchers feed them live prairie dogs so they can practice hunting.
Unlike the indoor cages the ferrets lived in while in captivity, the outdoor pens give black-footed ferrets the chance to feel rain, see the sky, and learn what life on the prairie is like.
Now about 1,000 black-footed ferrets are back in the wild. Fifteen live in Montana's Charles M. Russell National Wildlife Refuge, where Matchett works. He and his co-workers keep track of the ferrets, as well as other wild prairie animals including bighorn sheep, mountain lions, and elk.
TOUGH ROAD AHEAD
Despite their amazing comeback, black-footed ferrets aren't out of the woods yet, says Matchett. Sylvatic plague is still a threat, and ranchers still don't want too many prairie dogs on their land.
Matchett says scientists are making headway against the plague: They vaccinate all captive ferrets for the plague before releasing them into the wild. Additionally, they apply pesticides to the networks of burrows that make up prairie-dog towns. This kills the fleas that spread plague where the ferrets hunt.
Changing ranchers' minds about prairie dogs is harder. The federal government plans to begin paying ranchers to let prairie dogs live on their land--giving ferrets an opportunity to live there too.
"We have come a long way, and we've learned a lot," says Matchett. "I'm very optimistic that if we keep working, we'll be able to help this species recover."
UNDER THE PRAIRIE
Black-footed ferrets rely on prairie dogs. The ferrets eat them and then take over the burrows that the prairie dogs lived in. Prairie dogs sleep, raise their young, and hide from predators in a maze of burrows, called a town. Many other animals also depend on prairie-dog towns.
BABY'S ROOM: Newborn prairie dogs are born blind, so they're vulnerable to predators. For about six weeks, they stay safely in their burrow.
SQUATTERS: Many animals, like these cottontail rabbits, move into burrows that prairie dogs have abandoned.
STANDING GUARD: Mounds of dirt serve as lookouts for prairie dogs. When the guard, called a sentry, spots a threat, he alerts others with a special screech and then dives inside to hide.
HOSTILE TAKEOVER: Ferrets make themselves at home in the burrows of prairie dogs they've eaten.
ROAD MAP TO RECOVERY
Scientists are reintroducing black-footed ferrets to parts of their former 1.3 million square kilometer (502,000 square mile) habitat.
FROM CAPTIVITY TO THE WILD
 There are six ferret breeding centers in the U.S. A mother gives birth to a litter of three to four kits each spring.
 SAFE HAVEN: The kits live in indoor cages for 90 days, until they're big enough to catch prairie dogs.
3 ON THE PROWL: Outdoor pens protect young ferrets from predators for a month while they practice hunting their own meals.
 READY FOR RELEASE: A biologist releases a black. footed ferret into Wind Cave National Park in South Dakota.
WHAT DO YOU THINK?
Is it worth the time and money to try to save species from extinction?
OTHER ENDANGERED MAMMALS IN NORTH AMERICA
GIANT KANGAROO RAT
They are now found in only a 13-square-kilometer (5-squaremile) area in California--2 percent of their original range. Farms take up the rest of their former land.
Only a few hundred are left in the world. Researchers in North Carolina are trying to boost their numbers with a captive-breeding program like that used for ferrets.
The fur trade almost wiped them out by the early 1900s. Now nearly 73,000 live in Alaska. Thousands more live elsewhere, but disease now threatens sea otters around the world.
The U.S. Fish and Wildlife Service lists two species, the Sierra Nevada and the peninsular bighorn sheep, as endangered. Both live in California and are rapidly losing their habitat.