Black-footed Ferrets depended almost completely on Prairie Dogs. Weasels and polecats are generally active day or night and are little bothered by weather because they hunt primarily under ground or under the snow. All mustelids have anal glands with powerful musk. A little musk is passed with the fecal mass, which is carefully placed as a sign post where passing individuals are likely to find it. Almost all mustelids will spray in defense, although the skunk is the champion.
Ferrets are voracious predators and their kills are often larger than they are.
A single family of polecats can consume thousands of voles, mice, rats and rabbits in a single year. They are not necessarily effective in keeping the numbers of these prey animals down because the prey animals breed faster and their numbers increase more rapidly. The polecat population gradually increases and they are very effective in the suppression of any prey species over carrying capacity. This cyclic fluctuation of predator and prey populations is typical. Because the Black-footed Ferret was a true specialist and so dependent upon the Prairie Dog, wherever man controlled the Prairie Dog population, the ferret died out.