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NEW CHANCE FOR FERRETS? The most endangered
mammal in the
United States may get a vital boost—in Mexico - black-footed ferret
by Christie Aschwanden
A TINY, BLACK NOSE darts up through a prairie dog hole and back down so fast
it seems imagined. A few seconds later, an entire head pokes up, and a pair
of
curious black eyes gaze out. Picture a furry eel with legs and a face
resembling
a baby raccoon's, and you get a sense of the black-footed ferret.
This one can smell today's meal-prairie dog-resting on the soil just beyond
the safe reaches of the burrow, but it hesitates, scanning the scene for
signs
of danger. Finally, it makes its move. With the grace of a snake and the
speed
of a cheetah, it snatches the rodent in its teeth and yanks it into the
burrow.
The whole process is over in the blink of an eye.
This is no wild ferret, however. It was born here at the National
Black-Footed Ferret Conservation Center run by the U.S. Fish and Wildlife
Service (FWS) in Sybille, Wyoming, northeast of Laramie. And presently it is
attending a boot camp of sorts. The prairie dog it snatched was already
dead,
and the entire food-catching exercise is part of a training program to give
the
ferret a taste of the wild before it's shipped off to the real world-to
Mexico,
for what scientists say is the most ambitious attempt yet to save North
America's most endangered mammal.
In fact, its journey south-part of a plan in which Mexico is helping to
rescue the species-may be one of the black-footed ferret's last chances for
survival until habitat for its prairie dog prey is restored in the United
States. This September, if all goes as planned, researchers will release
between
75 and 110 of the animals in northwestern Chihuahua. Their far-reaching plan
aims not only to restore the ferret, but also to save a key remnant of an
imperiled grassland ecosystem that once stretched endlessly across the
continent.
Species on the Brink
With dark, liquid eyes, black gloves and dramatic eye masks, black- footed
ferrets are elegant hunters. Their slender bodies stretch out 20 to 24
inches
long (males are larger than females), including a sleek, black-tipped tail.
Their eponymous black legs and feet stand in stark contrast to their dusty
buff
bodies. So skillful are they in wielding their extra-long canines that
prairie
dogs, which sometimes dwarf them in size, make easy prey.
The ferret's survival has forever been entwined with that of the prairie
dog,
a foot-tall rodent that makes up about 90 percent of the predator's diet.
Poisoning, shooting and plague have depleted prairie dog populations. With
this
food source down and their own habitats declining, ferret numbers have also
plummeted over the years. In 1967, black-footed ferrets became charter
members
of what was to become the U.S. Endangered Species List.
Since then, long-term prospects for the ferret have lurched from pessimistic
to optimistic and back again. By the mid-1970s, the species had virtually
disappeared, and biologists feared it had joined the growing list of extinct
species. Then came some good news. In 1981, a small group was discovered on
a
ranch near Meeteetse, Wyoming, and researchers began to study them in their
natural environment. Four years later came near disaster: Canine distemper
and
sylvatic plague struck these remaining ferrets, killing all but 18.
Not willing to squander their second chance at saving the species,
researchers mobilized the survivors and moved them to the captive breeding
facility in Sybille. Today, that facility-a state-of-the-art complex central
to
a $1-million-a-year species-rehabilitation program- houses about 170
black-footed ferrets bred from the original 18. Six other captive breeding
facilities elsewhere hold a total of about 110 more.
The fate of the entire species rests with the ferrets raised at these
captive-breeding programs, and even with human intervention their survival
is
hardly assured. "Without substantive restoration of prairie dog populations,
their situation is dismal," says Mike Lockhart, coordinator of the FWS
black-footed ferret recovery program.
A Shortage of Habitat
The problem for both ferrets and prairie dogs boils down to one thing:
habitat loss. "We know how to raise black-footed ferrets. We know how to
release
them. What we're lacking is good habitat," says Pete Gober, a FWS biologist
in
Pierre, South Dakota, and an expert on prairie dogs.
Rick Bachand, a biologist with the National Wildlife Federation's field
office in Boulder, Colorado, agrees. "Grasslands are perhaps the most
endangered
ecosystem worldwide," he says. "Of the native mixed- and shortgrass prairie
in
the United States, as much as 70 percent has disappeared in some states."
Black-footed ferrets evolved with prairie dogs in this once-vast but now
beleaguered landscape. As the grasslands gave way to ranches, farms and
subdivisions, black-tailed prairie dogs disappeared. Today, the ferret's
prey is
at only one percent of its historic numbers.
Researchers are still learning what makes good ferret habitat, but based on
previous reintroduction efforts, they estimate that a sustainable ferret
population requires a minimum of 4,050 hectares (10,000 acres) of somewhat
contiguous black-tailed prairie dog habitat. Lockhart says there are fewer
than
ten, and perhaps only five, suitable sites left in North America.
The best habitat is across the border where Mexico has something the U.S.
does not: the largest continuous black-tailed prairie dog complex left on
the
continent-in an area called Janos-Nuevo Casas Grandes, about 45 miles south
of
the New Mexico border. It is a hot and arid place shared with pronghorn,
golden
eagles, burrowing owls and ferruginous hawks.
To the south and west, the region is bordered by pi-on and oak forests of
the
Sierra Madre Occidental foothills, and to the north and east by arid
scrublands.
The vegetation is a mix of grasses, annual herbs and isolated patches of
mesquite, cholla, ephedra and yucca. In all, the prairie dog colonies cover
approximately 35,000 hectares (86,450 acres). "We have recorded 45 prairie
dog
towns ranging in size from 1 to 15,076 hectares," says Jess Pacheco, field
coordinator of Mexico's black-footed ferret reintroduction project.
Making Ferrets Wild
The Mexico release hinges on the survival of captive-bred ferrets, so
researchers are giving them a boost with a pre-release training program.
Living
in outdoor pens, complete with prairie dog burrows, the ferrets at Sybille
and
other centers learn to live underground and hunt prairie dogs like their
wild
ancestors did. "We used to think ferrets had adequate innate behaviors and
that
you could just raise them in captivity and then when you released them,
they'd
know what to do, but it turned out that wasn't the case," says Lockhart.
Researchers learned that lesson the hard way. The first ferret
reintroductions took place in Shirley Basin, Wyoming, in 1991, but several
problems hampered that effort, which was halted in 1995. For one thing, the
ferrets weren't very predator savvy, and naive ferrets made easy prey for
hawks,
eagles and other grassland hunters. "Coyotes have been the number one
predator
by far," says Dean Biggins, a biologist with the U.S. Geological Survey
(USGS).
These scientists turned to some creative methods to blunt the problem.
"Initially we tried things like robo-badgers [a radio-controlled, stuffed
badger] and dogs to teach the ferrets about predators, but none of that
stuff
really worked," says Lockhart. "So now we just give them an opportunity to
live
like ferrets-catching live prey and living in burrows, and that seems to
work
much better.
Biggins pioneered many of the current reintroduction methods. In 1991, USGS
tested several rearing strategies, one of which involved raising young kits
in
outdoor pens (complete with prairie dog burrows) starting when they were
about
60 days old. "The success rate was at least three- fold higher one month
after
release for pen-raised animals versus those raised in cages," says Biggins,
"and
eight months post-release, the pen-raised ferrets had ten-fold higher
survival."
Such outdoor "preconditioning" is now standard fare.
Scientists at Work
Predators aren't the only ferret killers. Sylvatic plague is even more
deadly. It can decimate a prairie dog town in no time. If the resulting food
shortage doesn't kill the ferrets, the disease itself will. Though
researchers
are busy working on vaccines for plague and canine distemper, such tools are
still a long way off. So far, the Janos region is plague-free, and
researchers
are optimistic the disease won't hinder the Mexico reintroduction effort.
Orchestrating the release has required extensive planning. The animals will
likely come from several different captive-breeding facilities and will be
either driven or flown to Mexico. Researchers have secured the special
permits
needed to transport them across the border. Once the ferrets are in Janos,
scientists will release them as quickly as possible to minimize stress.
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