Black Footed Ferret
The black-footed ferret was probably never abundant. Nonetheless, it used to be found across a broad swathe of the American short grass prairies, from Texas to beyond the Canadian border. It commonly made its home in prairie dog colonies (called towns), taking over part of the tunnel system for its own use as predator in residence. The prairie dogs (burrowing rodents of the squirrel family) made up over 90 percent of the ferret’s diet. A single ferret could survive on what it could catch in even quite a small town, but mothers raising families normally took up residence in larger colonies.
Mice and other small prey caught outside the burrow at night added to the ferret’s prairie dog diet. Black-footed ferrets do not gather in groups. Instead, they spread themselves out, often living about 3.5 miles (6 km) apart; the low density of animals presumably prevented them from overexploiting their food resources. The ferrets were so dependent on prairie dogs for both food and lodging that when-in the 20th century-prairie dog towns were wiped out wholesale to make way for farmland, the ferrets suffered along with their prey. In Kansas, a former prairie dog stronghold, over 98 percent of the prairie dog population was eliminated in less than 100 years. By the middle of the 20th century the ferrets were feared extinct, although there were reported sightings of individuals from time to time. A small population was even discovered in South Dakota, but the group had apparently died out by 1974.
Back from the Brink
In 1981 a black-footed ferret was killed by dogs on a ranch in Wyoming. Subsequent investigations revealed that a substantial wild population, numbering at least 129 animals, had survived there. The group became the subject of intensive study, but the white-tailed prairie dogs on which the ferrets were feeding had suffered a population crash as a result of disease, and the ferrets themselves had been struck down by an outbreak of canine distemper. The last 18 ferrets were taken into captivity as an insurance against total extinction. By 1987 there were no black-footed ferrets left in the wild.
An Uncertain Outlook
In captivity the ferrets’ numbers built up slowly, to 70 in 1989 and over 300 by the end of 1991-enough for some to be reintroduced to the wild. Over a period of three years 188 ferrets were released, most of which probably died soon afterward. However, the survivors produced at least six litters of young. The captive population continued to increase, and by 1996 there were at least 400 animals in various zoos and conservation centers. The United States Fish and Wildlife Service has since carried out new reintroductions, releasing ferrets in Montana, South Dakota, and Arizona. However, even in protected areas where prairie dogs are no longer trapped, shot, or poisoned, the future for the black-footed ferret looks uncertain.
The main problem confronting the species is genetic. The entire surviving population of black-footed ferrets derives from a small handful of animals-the descendants of those taken into captivity in 1987 and as a result is dangerously inbred. Normally such inbreeding leads to poor reproductive success and a reduced chance of survival. It remains to be seen whether the newly restored populations, themselves bred from only a few dozen animals, will overcome their problems and increase to form a viable population. Even if they do, it is unlikely that they will ever again be widespread or numerous, simply because their prairie dog prey has disappeared from most of its former range. The black-footed ferret lives in prairie dog burrows. Its underground life and nocturnal habits explain why it is so little known. Yet despite its elusiveness, the ferret leaves tracks that are easily seen in snow, and the animal itself can sometimes be spotted at night by flashlight.
Statistics:
- Family: Mustelidae
- World population: Probably fewer than 500, mostly in captivity
- Distribution: Formerly grasslands of the American Midwest from Texas to the Canadian border; reintroduced into Montana, South Dakota, Arizona, and Wyoming
- Habitat: Short-grass prairies; in prairie dog burrows
- Size: Length head/body: 15-24 in Breeding: One litter per year in March-April; (49-60 cm); tail: 5-6 in (10-14 cm). Weight: usually 3-4 (but up to 6) young born; young 32-39 oz (915-1,125 g)
- Related endangered species: Colombian weasel (Mustela felipei); European mink (M. lutreola); Indonesian mountain weasel (M. lutreolina); black-striped weasel (M. strigidorsa)
- Form: Sinuous, short-legged animal, about the size of a small cat; pale yellow in color; black legs, mask, and tail tip
- Diet: Mostly small rodents, especially prairie dogs, caught inside the prairie dog burrow. Mice and other small prey caught outside at night
