In the 1800s, farmers began moving to the Great Plains. There, they encountered prairie dogs. These rodents were seen as pests because they dug extensive underground burrows that ruined fields. Farmers, and later the U.S. government, carried out campaigns to eradicate, or get rid of, prairie dogs by poisoning them. Many prairie dogs also died from a deadly disease called sylvatic plague, introduced by rodents from Europe brought on ships in the early 1900s.
Without enough prairie dogs to eat, black-footed ferret numbers dwindled. By 1979, they were thought to be extinct. Scientists believed there were no more living individuals left in the wild. But in 1981, a Wyoming rancher’s dog came home carrying a surprise: a dead black-footed ferret. Conservationists discovered a group of about 130 of the animals nearby. However, within a few years most of the colony had died from sylvatic plague and another disease called distemper. Soon, only 18 of the animals remained. Scientists captured those individuals to breed in captivity.