The questions and answers here will help you better understand the black-footed ferret and the work that SCBI and collaborators have been doing to bring this species back from the brink of extinction.
Until the arrival of settlers, an estimated one-quarter of the landscape, or more than 100 million acres, was pocked with prairie dog burrows channeled deep into the soil in a maze of tunnels and chambers. The largest prairie dog complex recorded, in Texas, measured 100 miles long and 250 miles wide (more than twice the size of Maryland) and may have contained more than 400 million prairie dogs by one estimate. Ferrets slept, hid, mated and gave birth in these burrows, and prairie dog meat made up 90 percent of their diet.
When the plains were settled, ranchers saw these grass-eating prairie dogs as competitors to cattle and killed the prairie dogs by the millions. As prairie dogs disappeared, so did ferrets. In addition, sylvatic plague (similar to bubonic plague) spread quickly, wiping out both prairie dogs and black-footed ferrets. Prairie dogs are now found on just two percent of the approximately 100 million acres they once inhabited.
It is true that there are still sylvatic plague outbreaks in prairie dog populations in the western states and that habitat loss remains a serious threat. Scientists at federal agencies are testing ways to immunize entire populations of free-ranging prairie dogs and others are considering compensation programs that would provide incentives to landowners to manage both wild prairie dogs and ferrets. The current black-footed ferret recovery plan indicates that the black-footed ferret can be down-listed from endangered to threatened status when there are 1,500 breeding adults in the wild. The species can be removed from the endangered/threatened list when there are 3,000 adults in the wild. That there are about 1,000 ferrets now living in nature is a testament to real progress. If we continue at the same rate, we should meet delisting goals by 2020 and again by 2040.
SCBI works closely with the U.S. Fish & Wildlife Service to reintroduce ferrets back into the wild. The ferrets are sent to the National Black-Footed Ferret Conservation Center in Colorado to prepare for release into the wild, a process called “preconditioning.” Preconditioning involves familiarizing the animals with burrows (underground tunnels) to increase the chance that they will survive in the wild.
About 35 days after ferret kits are born, animal care staff at the conservation center gives them live prey. Their mother hunts the live pretty at this age and the kits themselves begin to hunt at about 2 ½-months old. Ferrets trained in preconditioning pens have displayed as much as 10 times greater chance of survival in the wild than those without any prior conditioning. All reintroduction candidates go through preconditioning for at least 30 days. Then they are placed in pens that simulate a prairie dog burrow system and have the opportunity to kill live prey (prairie dogs).
Field biologists with state, federal, tribal and nongovernmental organizations monitor wild ferrets through spotlight surveys—they use high-powered lights to see the animals’ reflected green eyeshine. Researchers implant a Passive Integrated Transponder (PIT) tag under the skin of all black-footed ferrets. The tags do not have moving parts or batteries and do not hinder the animal in any way. Once biologists spot a black-footed ferret through spotlight surveys, they must place a reader within 6 inches of the animal to read the PIT tag. They often use a specialized donut-shaped ring that fits over a burrow opening. When the ferret pops its head out of the burrow (and through the ring), the researcher can read the PIT tag.
Wild-born kits of released black-footed ferrets do not have PIT tags, making it more difficult to track them. In order to implant these animals, researchers must capture them using a specialized trap. The animals are anesthetized for about 30 minutes while researchers insert a PIT tag. They then release the ferret after it is fully awake.
There are currently 19 reintroduction sites in Arizona, Colorado, Kansas, Montana, New Mexico, South Dakota, Utah, Wyoming, Mexico and Canada.
For a map of the sites, visit: http://www.prairiewildlife.org/BFFsites.html
According to the USFWS, “Hundreds of species that rely on the prairie ecosystem will benefit from conserving the BFF. The grasslands that support ranching represent the continent's most diminished ecosystem type. The BFF, one of the rarest of North American mammals is an icon of endangered rangeland wildlife. The BFF Recovery Plan sets forth an achievable goal of 500,000 acres of occupied ferret habitat as the key to recovering this rare species and removing its federal endangered status. Achieving this will require enrolling 1.5 million acres in the program to provide buffers that accommodate expansion and contraction of prairie dog colonies and meeting the grazing needs of livestock operators. In securing the land to meet this goal, this effort will reduce rare species listings by achieving conservation objectives for the black-tailed, white-tailed and Gunnison's prairie dog, ferruginous hawk, mountain plover, swift fox and burrowing owl across large portions of 12 involved states. This outcome would reduce federal, state and private costs associated with rare species' legal status.”
There’s no doubt about it—it is a challenge. The small number of original surviving black-footed ferrets makes the long-term survival of the species difficult. The fewer animals in any given population, the more likely it is for relatives to reproduce, leading to inbreeding, which can cause animals to reproduce poorly and develop malformations and be more susceptible to diseases. Researchers originally set out to maintain 95 percent of the genetic diversity among black-footed ferrets for 50 years. The final 18 left in the wild represented the genetic diversity of 9 to 10 unrelated individuals, which, under ideal circumstances, would allow scientists to maintain more than 90 percent of the species’ genetic diversity. However, as time passed, some of the lineages from the surviving wild ferrets did not breed as well as others. So about 85 to 87 percent of the diversity remains. One of researchers’ highest priorities is using computer matchmaking to avoid inbreeding.
There are many challenges. The black-footed ferret is a seasonal breeder, which means that the males and females only mate during the spring, leaving a small window for breeding to occur. Females are induced ovulators, which means that mating itself causes the ovary to release its eggs. Sometimes the female is not sexually receptive to the male. Occasionally the female will mate with a male but will fail to become pregnant, despite showing all of the signs of gestation. When a female ferret’s hormone levels rise indicating pregnancy and she displays behaviors associated with pregnancy but does not produce kits, this is called a pseudo—or false—pregnancy.
Males also have fertility problems. Nearly half the population is unable to sire offspring through natural breeding. Males can be aggressive toward females or don’t figure out the proper positioning during breeding. Black-footed ferret sperm can also be poor in quality as a result of the gradual loss in gene diversity. SCBI researchers have addressed many of these issues by using artificial insemination.
Originally there was very little information available about the reproductive physiology of black-footed ferrets, so SCBI scientists first developed assisted reproduction techniques for black-footed ferrets using the common domestic ferret (Mustela putorius) and later the Siberian polecat (M. eversmanni).
Sadly, prairie dog colonies are still being bulldozed, animals shot at and poisoned, and neither plague nor distemper show any signs of letting up. At the same time, the many stakeholders who have played a role in conserving the black-footed ferret are committed to the original recovery plan’s goal of establishing at least 10 self-sustaining, free-ranging populations totaling about 1,500 animals. A landowner incentive program is also slated to start that could add as many as seven release sites per year (35 total). Additionally, a new vaccination program for prairie dogs could make an enormous difference in creating higher quality, sustainable release sites. Most importantly, the black-footed ferret will continue to serve as an example of a huge success among partners, demonstrating how science and captive breeding can rescue an endangered species.
At SCBI, our researchers will continue to breed those animals that are most genetically valuable, including using artificial insemination as necessary with fresh and frozen-thawed sperm. The production of kits from sperm frozen for 20 years certainly demonstrates the wisdom of banking biological materials. A high priority will be expanding the genome resource bank and increasing artificial insemination efficiency. Additionally, SCBI is dedicated to training the next generation of ferret conservationists. Given adequate financial support, we aim to underwrite graduate students conducting their Ph.D. dissertation on this species. We have already had two successful graduate students complete doctoral dissertations studying the biology of the black-footed ferret.
There are so many scary and disappointing stories about species today: extinctions, disease epidemics, continued loss of habitat and unsustainable populations. The black-footed ferret is one of the few examples of successful recovery involving partnerships among institutions (including zoos) and with a heavy emphasis on scientific discovery. The ferret should be used to illustrate what is possible in saving species.
Individuals can financially support our program through a gift. The work done at SCBI is done through a very modest core budget. We conduct all required research using funds generated through outside support. Our highest priorities are for support of trainees (our next generation of black-footed ferret conservationists) and for laboratory supplies and travel to field sites.
Posted September 2011