Black-Footed Ferrets: Life Behind the
Mask
by Alex Hawes
Conservation at the close of the 20th century:
A woman in lime-green scrubs, face muffled behind a white, paper mask, leans over an anesthetized black-footed ferret. The ferret’s slender abdomen has been shaved and sterilized with a butterscotch layer of Betadine, then distended slightly by air pumped through a tiny orange hose. A sharp antiseptic odor pierces the room.
The surgeon JoGayle Howard, reproductive physiologist at the National Zoo inserts a small metal laparoscope into the creature’s swollen abdominal cavity, while a camera mounted on the scope’s tip relays an image to a monitor positioned at the foot of the operating table. The picture shifts and zooms across a tangle of organs before finally focusing on two conjoining, pink tubes: the ferret’s uterus. Having received a hormone injection 24 hours earlier, the animal should just now be ovulating. Howard threads a 25-gauge catheter narrower than the needles used to draw blood from humans, but appearing as large as a crowbar on the screen through the patient’s skin and into one horn of the uterus. Satisfied with the needle’s position near the ovary, Howard pipettes 100 microliters of cloudy solution into the uterus, then removes the catheter and repeats the procedure with the other horn. Bluebelle one of only 520 black-footed ferrets left on the planet has just been inseminated.
Forty-one days later, the laboratory matchmaking bears fruit as five of Bluebelle’s white-furred babies emerge from the womb. The kits scramble blindly around their mom for the next month nursing, sleeping, nursing, sleeping before their eyes finally open.
The ferret population is now one percent larger.
To the casual observer, artificial insemination (AI) may appear intrusive, if not downright rude. But as black-footed ferrets (Mustela nigripes) rally from the very brink of extinction, there’s little time for romance. The Smithsonian National Zoo’s Conservation and Research Center (CRC) and other organizations have mounted a monumental campaign to save the ferret, one of the most endangered mammals in all of North America. The effort involves not just natural and assisted reproduction of ferrets in zoos and conservation breeding facilities, but training ferrets for a future back in the wild. Colony by colony, state by state, ferrets are slowly returning to their western haunts, inspiring hope for a restoration of the wild America that early European explorers encountered and later settlers nearly extinguished.
Little Room on the Prairie
Black-footed ferrets belong to the Mustelid family, a group of 64 musk-producing species of carnivore that includes badgers, wolverines, otters, and weasels. Ferrets’ powerful jaws characteristic of mustelids are adapted for the swift submission of prairie dogs, as well as the occasional mouse, ground squirrel, or bird. Their limber frames allow them to dart through bending burrow tunnels and brace against tunnel walls for leverage when seizing prey that often outweighs them. To fuel high metabolic rates, adult ferrets must eat a prairie dog every three to four days on average to survive.
A half-million or more black-footed ferrets once inhabited wide swaths of the North American grasslands, which stretched unbroken from southern Canada across the western Great Plains to northern Mexico. Until the arrival of white settlers, an estimated one quarter of this vast landscape more than 100 million acres was pocked with prairie dog (Cynomys sp.) burrows channeled deep into the soil in a maze of tunnels and chambers. The largest prairie dog complex, in Texas, measured 100 miles long and 250 miles wide (more than twice the size of Maryland) and contained perhaps 400 million prairie dogs by one estimate. Ferrets slept, hid, mated, and gave birth in these burrows, and prairie dog meat formed 90 percent of their diet.
Lewis and Clark reported an "infinite number" of prairie dogs during their journey west at the beginning of the 19th century. The explorers didn’t make note of any black-footed ferrets, however although these lithe hunters were likely lurking below ground, awaiting nightfall. John James Audubon and his naturalist sidekick, the Reverend John Bachman, officially "discovered" the black-footed ferret in 1851 when a fur trader forwarded them a pelt with the distinctive ivory and brown markings, black feet, and black-tipped tail from an outpost along the lower Platte River in Montana. No other ferret sighting or specimen was reported for 25 more years, and rumors spread that Aubudon and Bachman faked the discovery to bolster their landmark book, The Quadrupeds of North America.
Of course, Plains Indians already knew the black-footed ferret well, referring to the masked creatures as pispiza etopta sapa, or "black-faced prairie dogs," and using their pelts to adorn ceremonial outfits. But just as indigenous Amerindians were displaced by European colonists, so too were ferrets and their prairie dog prey. More than 98 percent of prairie dog habitat has vanished since John Deere invented the steel plow in 1837 and homesteaders headed West to stake claims and till the soil [see "Prairies: Rediscovering a Fragile Frontier," May/June 1999 ZooGoer]. Federally sponsored poisoning campaigns beginning in the early 1900s and continuing today further reduced prairie dog colonies, and ferret populations consequently plummeted. The black-footed ferret was listed as endangered in 1967, and no wild ferrets were seen between 1975 and 1980. The species was feared extinct.
Then one crisp September night in 1981, Shep, a ranch dog in Meeteetse, Wyoming, killed a small animal he found at his food bowl. The dog’s owners, Lucille and John Hogg, brought the unfamiliar creature to a local taxidermist, who recognized the masked bandit and promptly alerted wildlife officials. Biologists discovered a wild colony of black-footed ferrets nearby, and hope for the species soared.
But hope yielded to panic once again when flea-borne sylvatic plague struck the area’s prairie dogs in 1984, and the population of about 130 ferrets went into a tailspin. Thirty-one ferrets were counted at Meeteetse in September 1985, and a mere 16 the next month. Only two male and two female ferrets survived the winter; yet, miraculously, each female gave birth to five kits the following summer. For the Wyoming Department of Game and Fish, it was now or never. Wildlife authorities had captured six ferrets the preceding year, and decided to trap the remaining individuals rather than risk another winter die-off. Eighteen ferrets now existed on the planet, none in the wild.
A Few Steps Back from the Brink
Seven ferret babies were born at Wyoming’s Sybille Research
Facility near Laramie in 1987, followed by 34 more in the
summer of 1988. Yet a single fire or the outbreak of disease
could deliver extinction instantly, so facility managers decided
to split up the colony. Having shown success managing populations
of clouded leopards, maned wolves, and other endangered species,
the National Zoo’s Conservation and Research Center became
the first institution outside Sybille chosen to receive black-footed
ferrets. In October 1988, seven ferrets arrived at the Front
Royal, Virginia, facility.
Three generations removed from Wyoming, Bluebelle is the great-granddaughter of "Dean," one of the original 18 rescued from Meeteetse. As the total number of black-footed ferrets has blossomed through the breeding program to more than 500, scientists including the National Zoo’s Jon Ballou, a researcher specializing in small population biology have had to monitor carefully the ferret family tree in order to preserve as much genetic variety as possible, and stave off the ill effects of inbreeding. The Zoo’s Conservation and Research Center has played a unique role. Since 1995, CRC has focused on breeding reproductive "duds" individuals with valuable, under-represented genes that haven’t mated properly elsewhere. Breeding records maintained by the Black-Footed Ferret Species Survival Plan have shown that nearly half of male ferrets aren’t fathering offspring through natural breeding, thus limiting the genetic variation in the population. Many male ferrets perhaps befuddled by the opposite sex display aggression to female partners, or can’t figure out the proper positioning for mating. Every last ferret counts when extinction looms, and artificial insemination (AI) offers the last resort when sex the old-fashioned way fails.
JoGayle Howard and her National Zoo colleagues first developed assisted-reproduction techniques for black-footed ferrets using domestic ferrets (Mustela putorius), and later Siberian polecats (M. eversmanni), their closest relatives, as models. Like Siberian polecats, black-footed ferret females display few visible signs of estrus, veiling the proper timing for AI procedures. Instead, the animal care staff at CRC have begun testing the readiness of female ferrets for ovulation by monitoring changes in their vaginal epithelial cells. When these cells demonstrate the readiness of the ovary’s follicles to release an egg, veterinarians can administer a hormone to a female that stimulates ovulation. However, Howard discovered that the anesthesia necessary during AI procedures prevents sperm from being naturally transported through a ferret’s reproductive tract. She therefore developed a surgical insemination technique using a laparoscope essentially a miniature telescope that provides a view of a patient’s internal anatomy to guide sperm to a position near the ovary where fertilization could occur.
Scientists also rely on frozen sperm to broaden the range of individuals that can be paired through AI. National Zoo researchers, led by David Wildt, head of the Zoo’s Department of Reproductive Sciences, have perfected cryopreservation techniques to store the semen of a variety of species, including clouded leopards, cheetahs, and giant pandas. Cheetahs at zoos across North America have now been impregnated by frozen semen collected from wild individuals in Africa (while Jomu, a cheetah at the National Zoo, was produced by artificial insemination using fresh semen).
Artificial insemination using both fresh and frozen sperm samples has produced more than 70 black-footed ferret kits at CRC since 1996, the first year the technique was implemented. The 70 to 80 percent rate of pregnancy from AI has even outpaced that of natural breeding (63 percent). Artificial reproduction has one particular advantage: Technicians can first screen sperm collected for AI in order to determine the most viable samples. A view through the microscope may expose upwardly mobile sperm gliding along, as well as bent sperm swimming in circles like boats endlessly tacking or ones with bent tails traveling hopelessly backwards. If no viable sperm have been produced, one sees only motionless blotches of skin cells, resembling craters on the moon. No signs of life.
Poor semen quality, perhaps due to inbreeding, only partly explains the failure of many natural breeders to conceive. Research at CRC has shown that one-year-old ferret males, which actively mate with females, normally don’t produce sperm until near the end of their first breeding season. Yet the act of breeding can induce ovulation, triggering a biological response known as "pseudo-pregnancy" in which female ferrets ovulate without conceiving and refuse to mate with other males then actually begin building a nest. Ferrets breed during one short period each spring, so if a young male mates with a female, the female may lose her opportunity to bear offspring for an entire year. Fertility in female ferrets drops off dramatically after their third year of life, so the window of opportunity is narrow indeed.
Largely due to unsuitable suitors now being screened out, the number of births in ferret conservation facilities in 1998 jumped to 432, more than 20 percent above the previous year’s record. CRC alone has witnessed the birth of 186 black-footed ferrets over the past 12 years. Insight into the secret world of ferret reproduction is thus helping CRC and other facilities maintain the species’ genetic diversity, fortifying the ferret for a life back on the prairie.
"The glory of this place," says JoGayle Howard on a drive through CRC’s vast campus in the Shenandoah foothills, "is you have a reproductive endocrinologist, people studying ecology and habitat, and experts in zoo breeding for animals that need help in all areas. You learn all you can about that species, and then go on to a new species. But you have to admit, the ferret is the cutest!"
The Native Returns
All along, the end goal of the ferret recovery program has
been a secure future for wild ferret populations. By 1991,
the number of ferrets in breeding programs was approaching
200, so conservation biologists at the U.S. Fish & Wildlife
Service (USFWS) began preparing to reintroduce ferrets into
the state from which the species was originally rescued. That
year, a group of 49 ferrets scampered free into southeastern
Wyoming’s Shirley Basin.
Yet only a small proportion of the individuals first released survived from year to year. Brian Miller, now of the Denver Zoo, found that many ferret kits weren’t accustomed to seeking shelter and safety underground. Teaching ferrets survival skills was the solution. An experiment by Dean Biggins of USFWS demonstrated that pre-conditioning black-footed ferrets to a life in the wild improved their odds of survival by 30 percent. Staff and volunteers at CRC therefore set about recreating life on the prairie for their resident ferrets.
Building a home for black-footed ferrets, in essence, means building a home for prairie dogs. First, workers haul a five-foot-high mound of dirt into outdoor pre-conditioning enclosures. Then the prairie dogs are let loose. These master diggers immediately begin fashioning a burrow, and within weeks have developed an intricate maze of tunnels and below-ground chambers. Once their work is done, the prairie dogs are sent to construction duty elsewhere, and the burrow is ready for ferrets. From indoor enclosures in which they gave birth, ferret mothers can take their offspring through a door to the outdoor burrows once the kits have reached 45 days of age. Ferret families must occupy the burrows for several months before being ready to head West for reintroduction.
The more elaborate the burrow the better the enrichment, so burrows that have already been tunneled may need occasional "freshening up" by prairie dogs between stays by different black-footed ferret families. "It’s like organized musical chairs," says Linwood Williamson, facilities manager for CRC. With ongoing burrow construction, 24 total enclosures will be available soon for pre-conditioning, enhancing CRC’s capacity to prepare ferrets for a home back on the range.
Training for life in the trenches means learning about life in the food chain as well. Fifty days after birth, ferret kits and their moms receive live prey to teach them the hunting skills crucial for survival in the grasslands. At one point, CRC researchers even introduced their ferret cadets to "Robo-badger," a mechanical beast designed to instill fear of larger prairie predators like badgers and coyotes. Lampooned by one memorable Dave Barry column, the Robo-badger program was halted when the ferrets quickly saw through the guise and ignored the cybernetic predator’s antics. Nonetheless, during pre-conditioning, CRC’s ferrets soon spend most of the time below ground, only occasionally exploring the surface before returning to the safety of the soil. "That’s what you want. Anytime there’s a disturbance you want them to dive down into that hole," says Williamson.
The results of the program have been dramatic: Ferrets trained in preconditioning pens have displayed as much as a ten times greater chance of survival in the wild than those without any prior conditioning. Now all reintroduced ferrets must first complete prairie boot camp.
Ironically, conservation programs may be readying ferrets for reintroduction more quickly than land is available. In 1995, USFWS set a target of ten self-sustaining populations of 1,500 total ferrets by the year 2010. Today, seven sites exist in Wyoming, South Dakota, Montana, Arizona, and Utah and Colorado will receive ferrets for the first time this fall. Only South Dakota’s colony in the Buffalo Gap National Grasslands, however, is growing quickly. Not coincidentally, South Dakota contains the only ferret habitat free from sylvatic plague, a disease in prairie dogs with the same origins as the bubonic plague in humans. The plague can strike suddenly, as it did in Fort Belknap, Montana, in 1999, when a population of 153 ferrets plunged to only five after prairie dogs there contracted the disease.
Ultimately, the ferret will survive in the wild only if large colonies of prairie dogs persist. A petition filed by the National Wildlife Federation in 1998 aims to list the black-tailed prairie dog (Cynomys ludovicianus) as a threatened species under the Endangered Species Act, a move that has temporarily halted poisoning on 3.8 million acres of prairie dog towns within U.S. Forest Service and Bureau of Land Management property. In January 2000, the USFWS ruled that this listing was warranted, but has delayed final ruling on the species’ candidacy indefinitely due to more pressing needs.
Amid America’s creeping suburban sprawl, finding large patches of healthy habitat for prairie dogs and their ferret dependents presents an even greater challenge. Indeed, the best site for future ferret releases may sit south of the border in Mexico’s Chihuahuan Desert, which boasts a vast black-tailed prairie dog colony that could support as many as 6,000 ferrets, researchers speculate.
Restoring ecosystems from sea to shining sea will itself speed the return of individual endangered species like the black-footed ferret. This fall, ten ferrets preconditioned at CRC will be transported to a new release site on the Cheyenne River Sioux Reservation near Eagle Butte, South Dakota. As one such ferret leaves the acclimation pen behind and darts across the grasslands, she will be greeted perhaps by the bobbing heads of a pair of burrowing owls, the coiled cringe of a startled prairie rattlesnake, the shadow of a soaring golden eagle briefly eclipsing the sun, or the yip of a prairie dog snapping from its buddha-like pose in the warm rays. Prepared for the moment, the ferret will dash to a nearby burrow, paw at the dirt to enlarge its entrance, and vanish silently into the womb of the earth.
Nature reborn at the dawn of the 21st century.
more! Ferret them
Out
Giant Steps
Alex Hawes is Associate Editor of ZooGoer.
ZooGoer 29(5) 2000. Copyright 2000 Friends of the National Zoo. All rights reserved.
