New digs for the ferret? A multinational program to introduce an endangered species into Northeastern Mexico may stimulate future cooperative conservation projects across borders.
In all, List, an associate researcher at the National Autonomous University of Mexico's Institute of Ecology, and other wildlife biologists from Mexico and the United States released a hundred black-footed ferrets in the Janos region on four different occasions last fall. The animals, almost all born earlier in 2001, came from captive-breeding facilities in the United States and Canada. The releases are part of a $1.5-million-a-year, multi-agency and multinational effort to save black-footed ferrets from extinction and restore them to the wild. If the Janos release works, it could help revive a ferret restoration program that has run into problems in the United States. It could also have far-reaching implications for wildlife conservation in Mexico and for joint U.S.-Mexican programs along both sides of the border.
"This is an extremely important area for us in Mexico," says Gerardo Ceballos, professor of ecology and conservation at the National Autonomous University of Mexico in Mexico City. "This is the last large grassland in Mexico. Grasslands are endangered ecosystems throughout North America. The black-footed ferrets will help us preserve that ecosystem and all the species that depend on it."
Black-footed ferrets are long, slender animals with short legs. They are relatives of weasels, badgers, skunks, and otters. The only native North American ferret, black-footed ferrets are closely related to Asian ferrets. The common domestic ferret is descended from the European ferret, or polecat. Fully grown, black-footed ferrets measure twenty to twenty-four inches long and weigh only two or three pounds. With a black face mask, black feet, and a black-tipped tail that contrast sharply with their tawny bodies, the ferrets resemble masked marauders.
Little known, rarely studied, and seldom seen, black-footed ferrets are usually active only at night, spending most of their time hidden in underground burrows. As a result, they remained unknown to science until "discovered" by naturalists John James Audubon and James Bachman in 1851. The ferrets once ranged from southern Canada into Texas and from the eastern slopes of the Rocky Mountains across the Great Plains. They could be found virtually everywhere on the prairies where there were prairie dogs, squirrel-like rodents that once lived in huge communal towns from Canada to Chihuahua in Mexico.
Today, as then, black-footed ferrets depend on prairie dogs for food and shelter. At least 90 percent of a wild ferret's diet consists of prairie dogs. The nimble ferrets not only dine on the rodents, they also appropriate their unwitting hosts' burrows for their own use. Unfortunately, ranches, farms, and cities are often located where prairie dog towns once thrived. Further, ranchers and farmers in the U.S. West often view prairie dogs as vermin that compete with cattle and sheep for grass and whose diggings leave horses lame While scientists dispute those claims, they have led to government and private programs to eradicate prairie dogs. Poisoned, shot, and trapped, prairie dogs now occupy only 1 or 2 percent of their estimated 100 million acres in the United States a century ago.
As prairie dogs went, so, too, did black-footed ferrets. Probably never common, the ferrets were long considered one of the rarest of North American mammals. They were feared extinct in the 1960s and again after a rediscovered population in South Dakota disappeared mysteriously in the 1970s. Then, some 120 ferrets were found near Meeteetse in northwestern Wyoming in 1981. Despite high hopes and intense monitoring, the Meeteetse ferret population dropped precipitously following epidemics of sylvatic plague and canine distemper that swept through the Wyoming prairie dog communities in the mid-1980s.
Fearing that the species was again on the brink of extinction, scientists studying the Meeteetse ferrets captured the last 18 animals between 1985 and 1987. The ferrets were sent to a new captive-breeding facility built by the Wyoming Game and Fish Department (WGFD) in Sybille. Beginning with 8 kits in 1987, some 400 ferrets are born a year now, with about 300 surviving, at Sybille and six zoos in the United States and Canada. Today, the captive-breeding program keeps 240 adult ferrets for breeding. More than a dozen zoos display ferrets among their exhibits.
With sufficient black-footed ferrets in captivity to ensure the species' survival, the U.S. Fish and Wildlife Service (USFWS) and the WGFD began releasing animals to the wild at Shirley Basin in Wyoming in 1991. Starting with 49 kits that year, USFWS and its partners in ferret recovery--other U.S. and state agencies and private groups--have reintroduced more than 1,500 animals at Shirley Basin and seven other sites in six U.S. states over the last decade. Shirley Basin was chosen first because prairie dog numbers were still low at Meeteetse following the outbreak of sylvatic plague, a disease caused by the same microorganism responsible for bubonic plague in humans.
"We've brought the ferrets back through captive breeding, but that's not good enough," says Mike Lockhart, the USFWS's black-footed ferret recovery coordinator. "We have to return them back in the wild." But restoring ferrets is no mere matter of setting captive-born animals free. For ferrets to survive and even thrive in the wild requires large blocks of prairie dog communities. Although the scientists sometimes have to do with less, they prefer to release ferrets at sites with at least ten thousand acres of prairie dogs, an average density of twenty prairie dogs per acre and no more than one mile between separate prairie dog towns. Less acreage can work if prairie dog density is particularly high. A site should also be free of sylvatic plague, which not only can wipe out whole prairie dog towns, thus reducing the number of prey, but also can infect and kill ferrets.
Practical experience has also shown that black-footed ferrets do best among black-tailed prairie dogs. The Meeteetse and Shirley Basin ferrets lived in areas dominated by white-tailed prairie dogs, a species found in the high plains of northern Colorado and Wyoming. Perhaps because they inhabit richer grasslands, black-tailed prairie dogs live in more densely occupied towns. That means "the ferrets don't have to search as far for food," Lockhart says. USFWS and its partners now try to release ferrets only at sites occupied by black-tailed prairie dogs. The only release site now featuring white-tailed prairie dogs is a new one along the Utah-Colorado border.
Learning how to prepare captive-born ferrets for living in the wild also required some trial-and-error efforts. At first, the ferrets were kept in indoor facilities with nest boxes to simulate underground burrows, wooden floors for easy cleaning to minimize the risk of disease, and plastic tubes for tunnels. Not surprisingly, 90 percent of the first animals released to the wild died within a year, most killed by other predators despite prerelease conditioning. Later, ferrets scheduled for release were placed in outdoor pens, exposed to dogs and fake badgers or owls, and allowed to live in cages placed in prairie dog towns before actually being set free.
Now, following a series of comparative tests in the 1990s by Dean Biggins, a U.S. Geological Survey (USGS) wildlife biologist, black-footed ferret managers go one step farther. Ferret mothers and theft kits are placed in outdoor pens shortly after the latter are born. The pens come complete with dirt floors, burrows, and live prairie dogs. To eat, the ferrets must learn to kill. No ferrets are released to the wild until they do. More important, the ferrets learn that prairie dog burrows are safe places. Pen-reared ferrets spend less time on the surface, where coyotes and owls can easily get them. "There is something about seeing the natural habitat of a prairie dog town very early in life," Biggins says. "The ferrets need to get the right experiences early on. Cage-raised ferrets just don't get that."
But such methods are costly and time consuming. The breeding facilities have to build indoor and outdoor pens, capture and raise prairie dogs, allow the rodents time to build their burrows, and then closely monitor them and the ferrets. Still, such preconditioning allows scientists to take captive-born ferrets that were raised in natural pens to a release site and simply open the cage doors and let them go. Such "hard" releases require less intense management than ferrets raised in indoor pens require at the site.
Not only ferrets, but scientists, too, face dangers during the periods of monitoring and study. Once, Biggins was digging in a prairie dog burrow to retrieve a radio transmitter attached to a collar around the neck of a released ferret that had apparently died. The transmitters are used to track the animals' movements. Suddenly, he found himself face-to-face with a snarling badger. The badger had killed and eaten the ferret, and taken over the burrow. Biggins had to quickly scramble to get away from the angry badger. But he got the radio transmitter.
Whatever the dangers of monitoring black-footed ferrets, the new techniques have worked. Natural-raised ferrets have a threefold greater chance of survival in the wild thirty days after being released over caged-raised ones and a tenfold greater chance after eight or nine months, Biggins says. Take Conata Basin, a thirteen-thousand-acre prairie dog community that is part of Buffalo Gap National Grassland in southwestern South Dakota. There, says William Perry, a U.S. Forest Service ranger, the survival rate has risen from 30 to 74 percent three months after release and from 10 to 46 percent a year later.
As a result, more than 400 black-footed ferrets now live in the wild, although that number can fluctuate as kits are born in the spring and predators or disease later take their toll on young and old alike. Conata Basin, the most successful site, has at least 250 ferrets and probably more. About 90 percent of the ferrets at Conata Basin were born in the wild since the first release there in 1996. More than forty litters were recorded in 2000 and seventy last year. The Conata Basin population has been growing by 28 percent a year. As a result, no ferrets have needed to be released there since 1999. And 20 ferrets born in the wild at Conata Basin in 2000 joined 49 captive-born ones that were released on a new thirty-thousand-acre site on the nearby Cheyenne River Sioux Indian Reservation, also in South Dakota. It was the first time black-footed ferrets born at one release site had been captured and sent to help start another.
But, so far at least, Conata Basin stands as the only truly successful restoration site for black-footed ferrets. All other sites are stagnant or foundering, some with their ferret populations barely holding on. At Shirley Basin, for example, only 19 ferrets were found in a 2001 survey, although WGFD biologists think others may be living on adjacent lands not surveyed. Only about 20 or so were found at a release site at Badlands National Park in South Dakota and less than a dozen at Fort Belknap Indian Reservation in Montana. No one knows how many ferrets still live in Aubrey Valley in northwestern Arizona. More than 200 ferrets have been released at each of those sites. On the bright side, at Cheyenne River, about half of the 69 ferrets released in 2000 were still alive in the annual spring survey last year. More than 60 others were released in 2001, but it is too early to know how many survived.
"We just don't know all the subtleties that may affect ferret survival," Lockhart says. One problem, clearly, is sylvatic plague and adequate habitat. The disease has wiped out most prairie dogs at Meeteetse and Shirley Basin, although habitat seems to be recovering. Plans for a release site at Thunder Basin National Grassland in northeastern Wyoming have been abandoned, at least for now, because of plague. Plague may also have contributed to the loss of all 36 ferrets released at Fort Belknap in 1999. No further ferrets will be released there until the plague epidemic passes. Some scientists worry that plague in Wyoming and Montana could soon spread to black-footed ferrets and prairie dogs in other states.
Meanwhile, scientists at the National Wildlife Health Laboratory have been working since 1999 on a vaccine to protect black-footed ferrets from sylvatic plague. The vaccine would be injected into ferrets prior to being released to the wild, says Tonie Rocke, a USGS epidemiologist at the Madison, Wisconsin, lab. Rocke also hopes to develop a plague vaccine for prairie dogs that would be given in food placed near their burrows. Elsewhere, Richard Montali, chief pathologist at the National Zoo in Washington, D.C., has helped develop an improved vaccine for canine distemper for ferrets and other wild carnivores.
A second problem remains the war against prairie dogs. Acting at the request of local landowners, the Bureau of Indian Affairs poisoned nearly all prairie dogs on 300,000 acres of land on the Pine Ridge Indian Reservation in South Dakota in the late 1980s. Until then, the area was considered a prime black-footed ferret release site. Additionally, Kansas and some other states long have required private landowners to kill any prairie dogs found on their property. If they do not, local authorities can send agents to do the job and bill the landowner.
On the encouraging side, South Dakota no longer lists prairie dogs as pests. Thus, landowners are no longer required to kill the rodents. Adjacent landowners can sue in civil court, though, if they can prove damage. Even in Kansas, landowners are now required to rid their property of prairie dogs only if neighbors complain. The National Wildlife Federation petitioned USFWS to list the black-tailed prairie dog as a threatened species in 1998, but the agency said that, while the listing was warranted, it could not take action now because of other priorities.
A third problem concerns the lack of prairie dog communities of sufficient size to support a healthy population of black-footed ferrets. Both the Charles M. Russell National Wildlife Refuge in Montana and the Badlands National Park have only three thousand acres of prairie dogs, too small an area for ferrets. "Our key limitation is habitat," Lockhart says of the prospect for ferret restoration in the United States. Such limitations may force USFWS and its partners to use smaller sites or ones with white-tailed and other prairie dogs. "We can't give up on those sites," says Pete Gober, a USFWS wildlife biologist and former ferret coordinator based in Pierre, South Dakota. "Beggars can't afford to be choosers."
That brings us back to the Janos-Nuevo Casas Grandes region of Mexico. "Janos is the best, unspoiled land for ferrets left," declares Rurik List, who helped study and restore black-footed ferrets to the wild in Wyoming in the early 1990s. "It can support a population large enough to sustain itself without intense management." U.S. ferret biologists agree. "It's an extremely important place," Lockhart says. "We are quickly running out of opportunities for ferrets. There are damn few sites left. Mexico is our best hope."
The Janos region consists of a dry, short-grass prairie bordering on Chihuahuan Desert thorn scrub to the north, east, and south, and on the Sierra Madre Occidental Mountains to the west. Privately owned ranches and communally run ejidos dot the area, along with Mennonite farms. In some areas, where ranchers and farmers have eliminated prairie dogs, mesquite woodlands have crept into the grasslands. Prairie dogs eat mesquite seedlings, but cattle and sheep do not. Cattle actually help spread mesquite by eating the pods and dropping the undigested seeds later when they defecate. Coyotes, gray and kit foxes, bison and pronghorn, and prairie rattlesnakes--all animals typical of the Great Plains--roam a fiat-to-rolling landscape dotted with occasional yuccas and agaves.
Gerardo Ceballos rediscovered Janos's black-tailed prairie dogs in the late 1980s. "Janos has the largest complex of prairie dog towns on the continent," he says, a judgment no one disagrees with. The area encompasses at least fifty thousand and perhaps as many as seventy thousand acres of prairie dogs, including one town that totals more than forty thousand acres. Better yet, no sylvatic plague has been found at Janos so far.
Two questions, though: Did black-footed ferrets ever live in the Janos area? If they did not, why release them to the wild there? "Nothing against trying [a release in] Mexico at the appropriate time with the appropriate safeguards and political support, but we haven't tried everything yet in the United States," argues Robert Oakleaf, nongame coordinator for the WGFD. "We really need to recover ferrets in their original habitat first."
True, no one has ever seen ferrets in the Janos region, nor are there any written records showing they once lived there. However, no one really looked for ferrets in Mexico until they were probably gone. Sixteenth-century Spanish conquistadors found ferrets in what is now New Mexico, and was once part of Mexico. Further, just about wherever black-tailed prairie dogs were found in North America, black-footed ferrets were too. So, scientists presume they were at Janos as well. Fossil remains of ferrets dating to the end of the Ice Age ten thousand years ago have been found both north and south of Janos.
Whether black-footed ferrets ever lived at Janos, they represent a conservation opportunity for Mexico. Ceballos hopes to use the ferrets to justify preserving more than 150,000 acres around Janos as a biosphere reserve, with about 44,000 acres as a core protected area. Ranching, farming, and some other human activities could continue outside the core area. The problem, Ceballos says, will be to raise $4 million in private money to buy ranch land before corporate agricultural companies move into what would become the biosphere reserve's core area. He hopes to have the money and enabling laws passed by the end of the year.
Beyond protecting habitat, the black-footed ferret has further significance for Mexico. "We have lost much of our wildlife," says Carlos Manterola, director of United for Conservation, a Mexico City-based conservation group. Successfully restoring ferrets in Janos will help promote wildlife conservation throughout the country. And, "by reintroducing black-footed ferrets now, in the future Mexico may be able to supply animals for reintroduction elsewhere," Manterola adds, including the United States.
Gabriela Chavarria sees the black-footed ferret release at Janos as a way to promote increased cooperation between Mexico and the United States to preserve wildlife. "This is a unique opportunity," says Chavarria, a Mexican native who is director of international programs for the National Fish and Wildlife Foundation in Washington, D.C. "This is the first joint reintroduction. We are working together to return an endangered species to the wild. This will open the door to other joint projects."
Jeffrey P. Cohn is a Washington-area writer and a previous contributor to Americas on science and conservation subjects.
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|Author:||Cohn, Jeffrey P.|
|Publication:||Americas (English Edition)|
|Date:||Jan 1, 2002|
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