Black-footed ferrets (Mustela nigripes) are one of North America’s most endangered mammals. They are members of the Mustelidae or weasel family, which also includes otters, badgers and wolverines. All members of this family have anal scent glands. Black-footed ferrets (ferrets) are North America’s only native ferret and they are a different species than ferrets found in pet stores. The animals sold in pet stores are European ferrets, a domesticated form of the European polecat.
Ferrets are 18 to 24 inches long, including a 5-6 inch tail. They weigh up to two and a half pounds. Black-footed ferrets are solitary animals except during the mating season and when mothers are raising their young. Mating occurs in the spring during a three day period. Litters of three to five kits are born in early summer after a six week gestation period. The average lifespan for a ferret is three to five years. Males and females look identical, although males are slightly larger.
Black-footed ferrets are highly specialized predators that depend on prairie dogs for food and shelter. More than 90 percent of the ferrets’ diet is made up of prairie dogs. Ferrets and prairie dogs live in prairie dog towns in underground tunnels called burrows.
In the late 1900s, a national effort to eradicate prairie dogs from prairies and grassland, because they were considered pests, resulted in a drastic decline in prairie dogs. This action also had extreme consequences for the ferrets due to their dependency on prairie dogs. By the late 1970s, no known black-footed ferrets lived in the wild, and the U.S. Fish and Wildlife Service (USFWS) considered declaring them extinct for the second time.
In 1981, the last remaining population of black-footed ferrets was discovered in Meeteetse, Wyoming on a privately-owned ranch. The USFWS began an intensive search and discovered a population of more than 100 ferrets. These animals were left on the ranch where they were closely monitored until a plague and canine distemper outbreak caused population numbers to plummet to 18 individuals. These last remaining ferrets were trapped and a captive breeding program was started in several North American zoos. Only seven of the 18 individuals that remained were suitable for reproducing, so all of the ferrets used for reintroduction efforts today originate from these founding animals. After a 60 year absence in Arizona, the Arizona Game and Fish Department (AGFD) began reintroducing black-footed ferrets in the state in 1996. With the release of 35 animals, Aubrey Valley, outside of Seligman, Arizona, became the fourth reintroduction site in the United States.
The primary goal of the Arizona reintroduction effort is to establish a free-ranging, self-sustaining population of black-footed ferrets in the Aubrey Valley Experimental Population Area (AVEPA). Other goals include managing ferrets and their habitat in a manner that will not negatively impact the lifestyles and economy of local residents, and establishing a second ferret reintroduction site in Arizona.
Black-footed ferrets require prairie dog burrows for shelter. Prairie dogs use prairie and grassland habitat ranging from the mid-west to the western United States. They are considered a key indicator species for the health of prairie and grassland habitat. In addition to the black-footed ferret, many species reside in prairie dog burrows including burrowing owls, snakes, lizards, mice and a variety of insects.
Gunnison's prairie dogs mainly occur in Plains Grassland and Great Basin Grassland in Arizona, north of the Mogollon Plateau and south of the Colorado River. The dominant vegetation in these biotic communities is blue grama, mixed with galleta grass, Indian rice grass, and other grasses.
There are five different species of prairie dogs in North America. Currently, the Gunnison’s prairie dog is the only species found in Arizona. The black-tailed prairie dog was previously found in south eastern Arizona, but was extirpated in the early 1900s.
The black-footed ferret was one of the original animals placed on the endangered species list in 1967. Loss of habitat and their susceptibility to plague and canine distemper has contributed to their decline over the years.
The reintroduction effort in Arizona was initiated under a 10(j) permit, which designates the population as experimental and nonessential. This classification allows reintroduction efforts to occur without effecting land use practices in the Aubrey Valley, including hunting and ranching.
Arizona has served as a leader in introducing new methods that may increase ferret survival upon release. Ferrets bred in captivity must sharpen their survival skills before being released back onto the prairie. Animals intended for release are preconditioned in large, natural outdoor pens where they become acclimated to the grassland. The captive ferrets hone their hunting skills in the preconditioning pens and learn to avoid predators, increasing their chances of survival in the wild. Arizona was the first to use on-site acclimation pens for ferrets.
In the spring, captive ferrets are bred in the preconditioning pens. Because ferrets are solitary and territorial, biologists monitor the animals to know when they are ready to be paired together for breeding. After the animals are paired, they are monitored for a three day period and then separated.
In 2001, the release method was changed to include spring releases of pregnant females in mid-gestation instead of allowing females to give birth to their young in the acclimation pens. Spring release of bred females coincides with prairie dog births. This release strategy for pregnant females has become the preferred method in Arizona, as the “wild born” young are thought to have a higher survivorship rate than kits raised in acclimation pens and then released in the fall.
Ferrets select their territories based on high prairie dog densities, so biologists determine prairie dog numbers prior to releasing captive animals. They use the Density Mapping Method, which requires transecting through prairie dog towns while counting and recording the activity of the burrows using a global positioning system (GPS). The data and GPS points are downloaded to generate a map showing high quality prairie dog habitat.
These density maps are used to establish future release sites for pregnant females and to determine where to survey (or spotlight) for wild ferrets. [PDF, 974kb]
Biologists use a survey method known as spotlighting to search for wild ferrets to monitor the population. Because ferrets are nocturnal, searches are conducted at night with high powered lights. Spotlighting events provide an excellent opportunity for the public to view these rare animals.
To learn more about spotlighting, volunteer opportunities and the most current spotlighting results, click here.