Black-Footed Ferrets Making a Comeback Through Artificial Insemination

By Bijal P. Trivedi
National Geographic Today
July 11, 2002
Reports of its extinction have been greatly exaggerated—twice.
After close to fifteen years of careful captive breeding and boot camp,
the black-footed ferret may be making a comeback. The recent birth of
the 100th ferret via a new artificial insemination technique was a small
but significant conservation milestone along the road to recovery.

Black-footed ferrets, which were listed as endangered in 1967 and were one of the first mammals listed under the Endangered Species Act of 1973, were already considered extinct by 1979. But in 1981 a ranch dog in northwestern Wyoming killed one that had tried to eat from its bowl. In 1984 a small population was discovered in Meeteetsee, Wyoming, but within a year canine distemper had infected the colony and threatened to wipe out every last ferret. Biologists mounted an emergency effort to rescue the species and snatched 18 of the animals from the jaws of extinction, including the very last known member of the species. All black-footed ferrets bred in captivity in North America are descendents of these 18 animals.

Snatched From the Jaws of Extinction

In 1986 the American Zoo and Aquarium Association established a Species Survival Plan for the ferret that involved captive breeding under strict genetic guidelines. Rules were created to prevent as much inbreeding as possible.

"Tremendous attention was paid to ensure that we were never breeding cousins or brothers and sisters," said Samantha Wisely, a new postdoctoral fellow at the National Zoo in Washington, D.C., who studied the genetics of this captive-bred population. Her study of genetic markers reveals that over the last 15 years "they have done a tremendous job of conserving the genetic diversity of these 18 animals."

"The main reason to use artificial insemination [AI] is to keep genes in the population," said Jo Gayle Howard, an animal reproduction specialist at the Smithsonian National Zoological Park and its Conservation and Research Center (CRC) in Front Royal, Virginia, who pioneered the new technique. From early breeding efforts Howard noticed that more than 50 percent of the males didn't sire offspring. Some males were behaviorally incompatible, some tried to fight and kill the females, and some just didn't know how to breed, said Howard.

"If we let those males who don't breed die without any representation in the population, we're going to lose their genes," said Howard.

Males from breeding programs around the country that are deemed the "most genetically valuable"—those which have not bred and not contributed to the gene pool—are sent to Virginia for AI.

"This is the only endangered species for which assisted breeding has become routine," said Howard. Artificial insemination has been tried in many endangered cats, for instance, but none with the same degree of success. Using AI, Howard gets a 70 percent pregnancy rate—about the same as from natural breeding. "So we couldn't ask for better than that."

Howard's AI technique differs because it employs a surgical approach. She uses a laproscope to guide a needle directly to the duct leading from the ovary to the uterus where the sperm await ovulation.

Ferret Boot Camp

Breeding isn't the only challenge. The survival plan also requires that captive-bred ferrets go to boot camp to increase their chance of survival.

Boot camp consists of a pen with special dirt where prairie dogs are introduced to dig custom burrows. The prairie dogs are removed and replaced with ferrets and the 60-day-old kits. The ferrets immediately take the babies into the dark burrows and they literally grow up in the hole. Kits that grow up in the burrows have a 10 percent greater chance at survival in the wild.

Then the prey is introduced. Black-footed ferrets eat only one thing—prairie dogs. Kill the prairie dogs and you kill the ferret. This was actually the main trigger for their demise. In the 1920s and '30s ranchers tried to eradicate prairie dogs from grazing land because they believed they competed with cattle for grassland. Poisoning and sport shooting these animals is still legal in most states.

But prairie dogs are usually twice the size of a ferret, so at the breeding facilities ferrets are first trained to kill hamsters.

"If they can kill a hamster then we think it's safe to put a prairie dog in there. But the Fish and Wildlife regulations say that these animals have to kill a live prairie dog before they go for reintroduction or they don't go," said Howard.

Robot Badgers, Mechanical Eagles

There were also attempts to familiarize the animals with predators like badgers and eagles. A battery operated robotic badger on wheels covered in a real skin was rolled through the tunnels to simulate a threat. A swooping mechanical eagle was also used, but the ferrets quickly figured out the robots were fake and didn't run.

The ferrets are hardwired with instinct. They see a prairie dog and they know what they are supposed to do. They open their mouth wide enough to clamp down on the throat of a prairie dog, which is typically twice its size, and suffocate it, said Wisely.

Since 1987 nearly 4,000 ferrets have been bred in captivity, of which 1,400 have been released at eight sites, with the newest in Chihuahua, Mexico, said Paul Marinari, Fish and Wildlife biologist at the National Black-Footed Ferret Conservation Center in Laramie, Wyoming. Ferrets are fairly short-lived, with a life span of only 3 to 4 years in the wild and recent surveys reveal that the total wild population is somewhere around 300 to 350. The number could rise after the surveys in September and October.

Animals in the wild now outnumber those in breeding programs.

Continued Supervision

Currently the only self-sustaining black-footed ferret population is in Conata Basin/Badlands in South Dakota. Last year there were about 100 wild kits born here—we were actually able to skim off some of these and release them at other sites, said Marinari.

Before settlers arrived, scientists estimated that there were about five billion prairie dogs burrowing around in North America, and about five million black-footed ferrets, said Scott Weidersaul, naturalist and author of The Ghost with Trembling Wings, which devotes part of the book to the plight of the ferret. The animals ranged from northern Mexico to southern Canada and west of the Rocky Mountains through the Midwest grasslands.

The greatest challenge is finding a release site with a protected prairie dog population free of disease, especially sylvatic plague—the animal equivalent of bubonic plague for which there is currently no vaccine—and that is becoming harder to find. "At least in the foreseeable future black-footed ferrets will require ongoing, and intense management," said Weidersaul.

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