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A Future for Ferrets

In 1987, scientists gathered the last black-footed ferrets from the wild. today, there are 19 wild colonies of these endangered animals.

By Cristina Santiestevan

In the corner of a concrete-and-wire enclosure sits a blue plastic storage box. Inside it are five miracles of modern science. Six, if you count their mother, Jambalaya, who pokes her head out to scold us.

This blue storage box—modified with air holes and a ferret-size entrance—is inside the quarantined small animal house on the Front Royal campus of the Smithsonian Conservation Biology Institute (SCBI). The box is home to a litter of black-footed ferret kits. Born on April 15, they were the first litter born at SCBI-Front Royal in 2011.

common cuttlefish

Kits born in 2010. (Mehgan Murphy/NZP)

The kits chatter and hiss when Lawrence Layman, the senior ferret keeper, removes the lid from their box. As adorable as they look, these ferrets are not cuddly. “If I picked them up, they would bite me,” explains Layman. “They stay pretty wild, and that’s the way we prefer it. Especially if they’re going to the wild.”

They have no way of knowing it, but these fierce little kits represent three decades of intensely managed black-footed ferret conservation. Thirty years ago, they were thought to be gone forever. No other species has recovered from such a close dance with extinction.

Phantoms of the Prairie

Black-footed ferrets have never been especially common. Although they were long known to Native Americans, the species was not officially recognized by scientists until 1851, when naturalists John Audubon and John Bachmann published a description based on a single specimen. A quarter of a century would pass before another individual was found, fueling suspicion that the species was nothing but a hoax.

By the early 1960s, scientists once again doubted the existence of black-footed ferrets. The species was presumed extinct, victim of a rapidly changing prairie landscape. Then, in 1964, a small and isolated population was discovered in southwestern South Dakota. But, only a decade after its discovery, this ferret colony mysteriously disappeared. A small remnant population of ferrets lived in captivity at the Patuxent Wildlife Research Center in Laurel, Maryland. They were believed to be the last living representatives of the species. When the last of these died in 1979, the black-footed ferret was once again declared extinct.

Two years later, a ranch dog caught and killed a ferret near Meeteetse, Wyoming, allowing the discovery of what truly became the last black-footed ferret population on Earth. Biologists spent several years observing this population’s behavior and growth as its numbers climbed to approximately 130 individuals.

Then, in 1984, disaster struck. Sylvatic plague and canine distemper swept through the colony, killing countless prairie dogs (the ferrets’ primary prey species) and nearly every ferret in the population. Scientists feared they were about to witness the extinction of blackfooted ferrets again, and likely for the last time. Rather than lose the species, they decided to capture the remaining ferrets and launch a captive-breeding operation. It took two years, but biologists caught the last of the wild black-footed ferrets in 1987. The entire species had been reduced to 18 captive individuals—mostly relatives—who were transferred to the Sybille Wildlife Research and Conservation Education Center in Wyoming.

This was a unique situation: a charismatic species on the edge of being lost forever. Would it be possible to save an animal with such a narrow population base, particularly when scientists had scant information on the biology of the species, including how to breed it in captivity?

The answer came in the form of partnerships involving hundreds of people from varied institutions, including the U.S. Fish and Wildlife Service, state wildlife agencies, universities, and zoos (the National Zoo among them). The first step involved workshops conducted in Wyoming and facilitated by the Conservation Breeding Specialist Group of the IUCN’s Species Survival Commission.

SCBI scientists Jon Ballou and David Wildt were some of the first advisors in creating what would become a successful recovery program. Ballou helped lead the computer modeling to produce data on how a small population might eventually result in sustainable, reintroduced populations. Meanwhile, because it was crucial for every animal to reproduce, Wildt provided guidance on how modern tools in assisted breeding (such as artificial insemination) could potentially play a role in maintaining healthy populations.

ferret kit

One of 670 ferret kits born at SCBI-Front Royal Common cuttlefish (Mehgan Murphy/NZP)

Population Explosion

In 1988 SCBI (then known as the Zoo’s Conservation and Research Center) received eight ferrets from Sybille. By then, several litters of ferret kits had already been born at Sybille, and the ferret recovery program—managed by the U.S. Fish and Wildlife Service—was eager to start several new captive colonies to reduce the risk of losing the entire species to a disease outbreak or other catastrophe. “We were the first facility outside the state of Wyoming to receive ferrets,” says Wildt, who heads the Center for Species Survival at SCBI. “This largely was because of our earlier involvement in developing the ferret recovery plan and also because we had a stellar record of breeding a variety of small-sized and basically unstudied mammal species.”

In the beginning, the ferrets were a bit of a mystery. “We had very limited knowledge about basic husbandry for this animal, including about nutritional and veterinary needs,” explains Wildt. “There also essentially were no data in the literature on the reproductive physiology of the species. In fact, only one publication existed on the subject of the common European ferret. So our scientists had a terrific, and somewhat daunting, challenge.” Thus began decades of hypothesis testing and studies by SCBI’s reproductive physiologists, endocrinologists, and veterinarians to create a body of scholarly knowledge. “That has been the key,” adds Wildt, “and the perfect example of how basic scientific information can be transformed into fuel to energize and create a successful captive-breeding program.” In less than 30 years, more than 6,500 ferrets have been born in captivebreeding facilities across the United States and Canada. And this—the production of more ferrets to return to the wild—is the ultimate goal.

But quantity is worth nothing without ensuring genetic quality. Male and female ferrets were—and still are—paired with one another based on their genetic history. This reduces the risks of inbreeding and helps maintain the genetic diversity of the It took two years, but biologists caught the last of the wild black-footed ferrets in 1987. The entire species had population. And this “heterozygosity” is everything. Without diversity, a population may quickly express negative traits (for example, abnormal sperm or a retained testicle) that then are passed from one generation to the next and can eventually reduce fitness and survival. Of the 18 individual ferrets in the founding population, many were closely related. In other words, their genetic diversity was exceptionally low.

“It was really essential that all ferrets in the original founder population have the opportunity to reproduce,” explains Wildt. In most cases, this required nothing more than introducing a male and a female, and allowing natural breeding—always the preferred method. But ferrets, like people, can have partner preferences, so sometimes these “managed dates” were less than successful with poor animal positioning or just outright aggression. What to do then?

At the time of SCBI’s initial work with black-footed ferrets, artificial insemination (AI) was commonly used in humans and livestock. But at that time, no one had considered the idea of inseminating a wild animal smaller than a house cat for the purpose of species recovery. With newly discovered basic data on the reproductive biology of the black-footed ferret, SCBI took on the task of applying AI as a method of routinely producing young.

JoGayle Howard

Reproductive expert JoGaylke Howard freezes ferret semen for later use. (Jessie Cohen/NZP)

Every year, SCBI received the most genetically valuable ferrets that had failed to reproduce naturally. These became the priority for the “insemination team” led by the Zoo’s fertility specialist, JoGayle Howard. Over the years, she produced more than 140 kits by AI with fresh sperm, by far the most offspring ever produced “artificially” in an endangered species. Then, in 2008, Howard began producing ferret kits using previously frozen sperm, including a sample from one of the original founders captured in the early days in Wyoming. “That was huge,” says Adrienne Crosier, the biologist who took over the ferret AI procedures after Howard’s death in March 2011. “It was like a founder being brought back to life and reproducing again, 30 years later.”

This year, Crosier and the insemination team (with the skills learned from Howard) produced another kit from sperm frozen in the 1990s. “The males that donated that sperm have all since passed away,” says Crosier. “It’s like resurrecting a male from the dead.”

Reintroduction Realities

Black-footed ferrets were lost from the wild in 1987, when the last individual was captured from the Meeteetse, Wyoming, population. In 1991, only four years later, they were back. Forty-nine juvenile ferrets were released into a prairie dog town in central Wyoming’s Shirley Basin. These ferrets produced at least two litters of wild-born kits in 1992 and another four litters in 1993. The population was also supplemented by additional reintroductions of captive-born ferrets in 1992, 1993, and 1994. A total of 228 captive-born ferrets were released into the Shirley Basin prairie dog town between 1991 and 1994. Since then, thousands more have been released into prairie dog towns from Canada to Mexico.

Reintroducing black-footed ferrets into the wild is no simple matter. They are remarkably specialized. Most predators hunt a variety of prey, and take shelter in a range of habitats. Not black-footed ferrets. They cannot survive without prairie dogs. These plump ground squirrels are the ferrets’ food and provide their burrow shelter, and their presence determines where black-footed ferrets can be released. Without prairie dogs, we would have no black-footed ferrets.

ferret in the wild

A ferret reintroduced into the wild. (Jessie Cohen/NZP)

This, in brief, is the whole story behind the decline of black-footed ferrets. Prairie dogs—and ferrets—once ranged from southern Canada to northern Mexico, with their subterranean colonies lying beneath more than 100 million acres. Today, their range, less than two million acres in total, has been reduced to a scattering of individual colonies that are often separated by miles of developed or inhospitable land. Between creeping suburbs and fiercely protected rangelands, there is little space left for prairie dogs or black-footed ferrets.

Even the wildest of places are not always safe for prairie dogs or black-footed ferrets. Canine distemper, spread by coyotes, foxes, and dogs, is fatal to ferrets. Both prairie dogs and ferrets are susceptible to sylvatic plague, carried by fleainfected rodents. It can rapidly wipe out an entire prairie dog colony. Because the spread of both diseases is unpredictable, biologists regularly vaccinate wild ferrets for canine distemper and sylvatic plague. Prairie dogs present a challenge, however. A colony may house hundreds or thousands of prairie dogs, an impossibly large number for traditional vaccines. Biologists are hopeful that a prairie dog sylvatic plague vaccine will soon be available in pill form, which would be much easier to distribute to an entire colony.

People, however, are black-footed ferrets’ greatest challenge. Prairie dogs may be essential to ferrets, but they are viewed as nothing more than a nuisance or a pest by many people. It is still legal to poison prairie dogs on private land, and some states even require poisoning prairie dogs, regardless of the landowner’s desires. This is exactly what happened when two neighboring Kansas landowners, happy to have prairie dogs on their land, volunteered to have ferrets released onto their properties. When word spread about the planned release, the county responded by spreading poison on both properties. “They hate prairie dogs,” says Layman, who explains that the two private landowners eventually won in court, and saw ferrets released onto their land on December 18, 2007. “It took several years, but they do have ferrets in Kansas now.”

Despite the challenges, the reintroductions continue. Since 1991, thousands of black-footed ferrets have been released into 19 prairie dog colonies, ranging from Grasslands National Park in Canada to the Chihuahua region of northern Mexico. Many of these populations are small and continue to be supplemented by reintroductions of captive-born ferrets, but they are wild. In total, there are approximately 1,000 black-footed ferrets roaming the wild today.

Altered Attitude

Of all the program’s many successes, the greatest of all has nothing to do with ferrets and everything to do with human attitudes. “Back then, 30 years ago, there were some really strong feelings against taking the last few animals and moving them into captivity,” says Wildt. “There were people in the field who would say that it would almost be better to have these animals go extinct than to have them go into captivity.”

This explains why the Meeteetse ferrets were left undisturbed until plague and distemper nearly wiped them out. Had the ferrets had been captured earlier, the founding population might had been as large as 130 individuals, rather than 18. From a genetic point of view, that is a huge difference. Some of the problems associated with inbreeding—kinked tails, low sperm viability, undescended testes—may not have been an issue if the founding population had been larger.

Anti-captivity bias has faded in recent years, thanks in large part to the remarkable rebound of black-footed ferrets. “You have this species that was once declared extinct,” says Wildt. “You bring it into captivity. You learn everything you can about its basic biology. You’re able to turn it around and release it back into nature.” Wildt believes these successes have already motivated biologists to respond more rapidly, and work more cooperatively, when species are in decline.

“The black-footed ferret is now this iconic example of what happens when you go through a population bottleneck,” says Wildt, who explains that the ferret is “the poster child for what can happen, even if you are down to the last few animals.” This may be the black-footed ferret’s greatest legacy.

What Next?

Despite its comeback, the black-footed ferret remains the rarest mammal in the United States. Its future in the wild is far from certain. Whatever the future may hold, this year is looking to be a very good one for the ferrets at SCBI. Last year, SCBI celebrated the birth of 50 kits—an annual record for the facility. This year has been better. SCBI has produced 51 young so far this year. Again, all of this is testament to the care and scientific and scientific approach taken by National Zoo staff.

As for the five kits born on April 15, their futures are now in discussion by the species managers. By winter, they will have left their blue box far behind. Some might have moved to another black-footed ferret breeding facility, where their genes will hopefully spread to another generation in the spring. Other may have settled into outdoor training pens at the National Black-Footed Ferret Conservation Center in Colorado, where they will learn to live like wild ferrets. Some may even have settled into a colony of wild prairie dogs, bringing a bit more wilderness back to North America’s prairies and grasslands.

 

—Freelance writer CRISTINA SANTIESTEVAN is a regular contributor to Smithsonian Zoogoer.

 

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Smithsonian Zoogoer 40(4) 2011. Copyright 2011 Friends of the National Zoo. All rights reserved.