Ferrets may reduce prairie dog numbers in small colonies by predation and by the disruption of prairie dog breeding activity caused by their presence in a prairie dog colony. Studies have shown a decline in prairie dog numbers in a part of a colony occupied by ferrets, but the total number of prairie dogs in the colony was not greatly affected. They use prairie dogs for food, and use the burrow systems for shelter and for raising young. During nine years of study in South Dakota in the 1970s and four years in Wyoming in the early 1980s, ferret litters were found only in prairie dog colonies. Individual ferrets have been found outside prairie dog colonies during periods of dispersal, however.
Loss of habitat is the primary reason black-footed ferrets remain at the brink of extinction.
Conversion of rangeland to agricultural and other uses, and prairie dog eradication programs have reduced ferret habitat to a small fraction of what once existed. Remaining ferret habitat is now fragmented, with prairie dog towns separated by large expanses of cropland and grassland unoccupied by prairie dogs. Some ferrets undoubtedly have died from eating prairie dogs that died or were dying from consuming poisoned grain distributed to eradicate prairie dogs. Limiting Factors Black-footed ferrets face several threats in the wild, the most serious being predators and diseases. Ferrets have reached nine years of age in captivity, but achieving three or four years of age in the wild is quite an accomplishment.