Endangered Mammals - The Black-footed Ferret

The black-footed ferret (see Figure 7.1) is a small furrow-digging mammal and member of the weasel family. FIGURE 7.1
Black-footed ferrets, once thought extinct, are now being successfully bred in captivity. A few reintroduced ferret populations are doing well. (U.S. Fish and Wildlife Service) Nocturnal creatures, ferrets help to control populations of snakes and rodents, including their primary prey, black-tailed prairie dogs. Black-footed ferrets once ranged over eleven Rocky Mountain states as well as parts of Canada. They have declined drastically because of the large-scale conversion of prairie habitats to farmland, and because their primary prey, prairie dogs, have been nearly exterminated by humans. Prairie dogs are considered pests because they dig holes and tunnels just beneath the ground surface. These can cause serious injury to horses or other large animals that step into them. (Some municipalities also poison prairie dogs in city parks, where burrow holes can trip and injure humans.) Poisons used to kill prairie dogs may also kill some ferrets.

Black-footed ferret populations had declined so greatly that the species was put on the Endangered Species List in 1973. However, prairie dog poisonings continued, and by 1979 it was believed that the black-footed ferret was extinct. In 1981 a ferret was sighted in Wyoming and discovered to be part of a remnant population. Rewards were offered for more sightings, and by the end of the year a few black-footed ferret populations had been located. These typically existed in close proximity to prairie dog populations in sagebrush-heavy areas. In 1985 ferret populations were struck by disease, and by 1987, only eighteen blackfooted ferrets were in existence. These individuals were captured and entered into a captive breeding program.

The captive breeding of ferrets has been reasonably successful. There are now core populations of 269 breeding-age individuals in five zoos in the U.S. and Canada as well as one Fish and Wildlife Service facility. In 1999 a total of 133 kits were born. The Fish and Wildlife Service has also tried to reintroduce black-footed ferrets in several states. Studies suggest that each population of black-footed ferret requires approximately 10,000 acres of black-tailed prairie dog habitat to survive. Unfortunately, prairie dogs are also in decline due to habitat loss and episodes of sylvatic plague, which have decimated many populations. Although some reintroductions have failed, two are doing well—one in National Forest habitat in Conata Basin/Badlands, South Dakota, and another in the Charles M. Russell National Wildlife Refuge in Montana. In 2000 there were already many more wild-born than captive-born ferrets at those sites. The Fish and Wildlife Service recovery plan for black-footed ferrets hopes to move the species from endangered to threatened status by 2010. This would require that 1,500 breeding adults exist in the wild in a minimum of ten separate locations, with a minimum of 30 breeding adults included in each population. Captive breeding and reintroductions of black-footed ferrets were organized by the Black-Footed Ferret Recovery Implementation Team, and involved twenty-six separate state and federal organizations, conservation groups, and Native American tribes.