Black-footed Bandits, Stealing Home
by Howard Youth
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All may seem tranquil above the surface of a prairie dog town, but danger lurks below. Deftly infiltrating a labyrinth of burrows with ninja-like stealth and speed, the black-footed ferret (Mustela nigripes) seizes sleeping prairie dogs by night, and rests in their burrows by day. While this mink-sized, tubular-bodied carnivore seems to have found itself a good niche, its specialized diet and behavior binds it to the misfortune of its once-abundant prey.

Ranchers have long considered prairie dogs (Cynomys spp.) competitors for the grasses eaten by their cattle and sheep, and complain that prairie dogs' burrow entrances pose a hazard to loping livestock. After more than a century of being shot, poisoned, trapped, and bulldozed, prairie dogs are now found on just two percent of the approximately 100 million acres they once inhabited.

black-footed ferret coming out of prairie dog tunnel
Black-footed ferrets live and hunt in prairie dog towns. (Randy Matchett/USFWS)

Populations of black-footed ferrets, burrowing owls (Athene cunicularia), mountain plovers (Charadrius montanus), and other wildlife closely associated with prairie dog towns vanished in turn. By 1964, the black-footed ferret, once a fixture in the western Great Plains from Canada to northern Mexico, was known to survive in just one area of South Dakota. By 1974, even this population was gone, leading many to conclude that the ferret, 123 years after its first formal description by John James Audubon and John Bachman, was gone forever.

The ferret resurfaced in 1981, thanks to a dog. After romping around on a ranch in remote Meeteetse, Wyoming, about 50 miles east of Yellowstone National Park, the canine carried home a long, sand-colored mammal with a blackish mask and tail tip, and black "stockings."The dog's owners sought wildlife officials' help in identifying the weird dead creature, and their inquiry led to the location of a back-from-the-brink population of about 130 black-footed ferrets in Meeteetse.

Three years later, sylvatic plague, the same illness known as Black Death in medieval Europe, killed off many of the Meeteetse-area prairie dogs, and canine distemper virus nearly wiped out the ferrets. (Although plague in humans is now easily treated with antibiotics, it can sweep through a prairie dog colony like wildfire.) Fearing another disaster, state and federal conservationists took the remaining 18 ferrets out of the wild and enlisted them in breeding efforts.

After the U.S. Fish & Wildlife Service (USFWS) published its 1988 Black-footed Ferret Recovery Plan, Smithsonian National Zoo scientists were invited to take a lead role in studying and breeding one of the most endangered carnivores in the world, work that continues 25 years—and 282 zoo-born ferrets—later.

Scientists at the National Zoo's Conservation and Research Center work with other zoos, land managers, and biologists to learn more about how the black-footed ferret breeds and to boost the species' chances through assisted-breeding techniques such as cryogenically preserving sperm and artificially inseminating females, to improve reproductive efficiency. (Zoo scientists developed reproductive science specific to the black-footed ferret by studying two of its closest relatives, the domesticated ferret, Mustela putorius furo, and the steppe polecat, Mustela eversmanii.) With artificial insemination, females can conceive young with males that would otherwise not be represented in the breeding program's gene pool, including males of underrepresented lineages.

While their overall goal has been to increase the number of young produced for potential reintroduction into the wild, Zoo scientists and their colleagues have learned many other important things along the way. For example, they found that black-footed ferrets lack Interleukin 6, a protein that plays a key role in regulating the immune system. Interleukin 6 inhibits inflammatory response to disease, and its absence in black-footed ferrets may explain why they often die from intestinal parasites that other ferret species survive.

Beginning in 2002, Zoo scientists also collaborated with organizations and other zoos on a survey of the health of black-footed ferrets at all reintroduction sites, including ferrets that had been released and those born in the wild. They found, among other things, that ferrets remain susceptible to sylvatic plague, which can wipe out their prey and potentially kill them too, and that reintroduced ferrets need to be vaccinated against canine distemper. After analyzing 253 different animals, the team found that populations at some sites, such as the Conata Basin in South Dakota, continue to do well, while others require periodic reintroductions, and others, such as those in Montana, are crashing.

black-tailed prairie dog
When prairie dogs' populations declined, so did black-footed ferrets' . (Gaby Gollub/FONZ)

Now, 25 years after the rediscovery of black-footed ferrets in Meeteetse, the future of one of the United States' most endangered mammals appears far more promising than it did in 1981. For one thing, the species' survival no longer rests with just one disaster-prone population. Today, about 550 wild black-footed ferrets live in six states within their former range—Arizona, Colorado, Montana, South Dakota, Utah, and Wyoming—and there is now also a small group reintroduced and living in Chihuahua, Mexico. Scientists hope that placing these animals in different parts of the species' once-wide range will increase their numbers and protect them from total annihilation if major disease outbreaks or severe droughts strike. In addition, almost 300 more ferrets are in various breeding facilities and about 20 others are on exhibit at zoos, bringing the total population of this once-lost species to about 870.

The situation, while promising, remains tense. Prairie dog colonies are still being bulldozed, shot out, and poisoned, and the twin threats of plague and distemper show no signs of letting up. The ferret's largest plague-free stronghold, Conata Basin, holds about half the remaining wild ferrets, but now lies at the edge of plague's advance. Conservationists are waiting to see what happens: If the disease threat becomes dire, they may capture the Conata Basin ferrets before plague ravages their food source and perhaps attacks them. Wildlife officials have already dusted the area with insecticide to reduce the population of fleas, which are vectors of the sickness.

While the USFWS lists the black-footed ferret as endangered, all of its known wild populations originate from animals born in the breeding program. These populations are designated "experimental and nonessential"by the USFWS, a status that sits better with private landowners, who are more likely to cooperate with government-supported conservation efforts if they know such collaboration won't strictly limit their land-use options.

Given the continuing challenges, habitat protection, zoo breeding, careful monitoring, disease surveys, and reintroductions will remain priorities as conservationists strive to meet goals set by the USFWS Black-footed Ferret Recovery Plan—namely, the establishment of at least ten self-sustaining, free-ranging populations totaling around 1,500 animals.

—Contributing editor Howard Youth writes on a variety of conservation-related issues.

ZooGoer 35(4) 2006. Copyright 2006 Friends of the National Zoo. All rights reserved.



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