Although they lived throughout the Great Plains, the ferret population has been falling ever since we first knew about them. One reason for this is that the ferrets are so dependent on prairie dogs, a species of ground squirrel. Not only are these rodents their staple food, the ferrets also cannot dig their own burrows and are squatters in prairie dog towns. When settlers moved west, many became farmers. They plowed under the prairie dog towns and hunted or poisoned many of the animals. Both the prairie dogs and the ferrets grew increasingly fewer.
Then, in 1981, a Wyoming dog named Shep found a ferret. Eventually, the animal was identified and its colony -- of about 130 animals -- found. However, this population quickly plummeted due to canine distemper and sylvatic plague. In 1986, the remaining 18 animals had to be removed from the colony. The ferret was extinct in the wild.
At this time, there were only fifty captive black-footed ferrets in the world. After years of captive breeding, the first place to reestablish a small colony was Wyoming in 1991. Now, there are fifteen established fesnyngs (or businesses: the name for a group of ferrets) in the wild, in eight US states as well as Mexico and Canada.
There are, however, still threats to their survival. Their close relationship with prairie dogs does not aid their recovery. Prairie dogs are often viewed as pests because they prevent farmers from growing crops in certain areas by rooting up the plants around their burrows. Their tunnels also make the ground less stable and more prone to collapse if animals are turned out to graze.
Because of these things, many people dislike prairie dogs. Even today they are hunted, both commercially and privately. To eradicate colonies, they are poisoned, which indirectly affects many other species. Two of the popular poisons, Rozol and the recently approved Kaput-D, contain chemicals that thin the prairie dogs' blood until they bleed to death. Not only is this horrible for the prairie dogs, any animal that eats them will encounter the same fate. Black-footed ferrets, swift foxes, American badgers, ferruginous hawks, and golden and bald eagles all prey on prairie dogs. An infected animal is easy to catch because it becomes unable to move quickly or control its motions, so many of these predators are suffering secondary poisoning. Additionally, mountain plovers and burrowing owls live and nest in prairie dog burrows and can also become infected.
Another threat to ferrets is disease, particularly sylvatic plague. Luckily, the animals can be immunized against the disease, and all ferrets born in captivity are required to be given two shots of the medicine. Although prairie dogs are also susceptible to this, it has been found more difficult to protect all of the wild colonies from the bacteria. One widespread method was to spray each burrow with flea-killing pesticides, but scientists realized that this was probably too expensive and hard to do and maintain. There had to be an easier way to accomplish this. Finally, they developed a medicine that could be mixed in with food left for the prairie dogs to eat. This also proved more efficient than the pesticides. Additionally, these studies will benefit other species susceptible to the sylvatic plague, both wild rodents and some pets.
There are now more than 1,500 ferrets throughout the established colonies, so the species has been upgraded from extinct in the wild to endangered. Although the number is low, it is still a success considering how few animals lived at one point. Black-footed ferrets are considered the most endangered mammal in North America, but the numbers are still rising to the extent that they may become relatively common over time. The current ambition is to establish ten breeding populations in the wild. When this is met, the ferret can be listed as threatened, instead of endangered. When this happens, the ferret will have returned.