The Black-footed Ferret has the narrowest range of ecological tolerance of any North American predatory mammal. They occur almost exclusively in prairie dog towns, most of which are located in shortgrass rangeland. They live in prairie dog burrows and prey on the squirrels and other occupants of the burrows. They are primarily crepuscular and nocturnal but may be seen above ground at any hour. In winter, they often remain in their burrows for up to a week at a time. As is true of many predators, population densities are relatively low. Black-footed Ferrets appear to be solitary. Usually only one individual or a female with her litter live in a prairie dog burrow. Although secretive, the presence of Black-footed Ferrets can be ascertained by snowtracking and the distinctive trenches that they excavate at the entrance to their dens.
Average longevity in the wild is short because of predation and other causes of mortality. Data on longevity are not available.
The Black-footed Ferret feeds primarily (more than 90%) on prairie dogs. They also consume mice, ground squirrels, rabbits, birds, snakes, and insects that they catch in and around prairie dog burrows, but these foods are ancillary to prairie dogs. Predation by Black-footed Ferrets evidently does not reduce prairie dog populations because ferrets only kill what they can eat (this reportedly averages approximately 100 prairie dogs per ferret per year). However, the presence of ferrets in a large prairie dog town may limit growth of prairie dog numbers and spread of the town.
Factors that influenced decimation of populations of the Black-footed Ferret included conversion of shortgrass prairie to agricultural cropland, use of toxicants to kill prairie dogs, fragmentation of large prairie dog towns, disease, shooting, trapping, and predation. In 1978 the skull of a ferret and some associated prairie dog remains were found at the entrance to a burrow in a colony in Gove County. The town had been poisoned the previous year, and new occupants evidently had cleaned the burrow before moving in. Ferrets are extremely susceptible to distemper and sylvatic plague, which can rapidly decimate a population. The primary predators on ferrets include Coyotes, raptors, and domestic dogs. Also, it should be noted that Black-tailed Prairie Dogs are formidable prey for the Black-footed Ferret, especially above ground, and are known to gang up on ferrets. This may be a cause of mortality in ferrets, especially young ferrets. Finally, deaths occur when ferrets disperse along roads.
Black-footed Ferrets breed when one year old during March and early April. Gestation lasts from 42 to 45 days, and litter size averages 3.5. Young remain in their natal burrow for about 42 days before venturing above ground. The female and her young remain together into August, and the young disperse in the autumn.