Scientific Name: Genus Mustela
Of the eight members of the weasel family known in Colorado, only two actually are called weasels: the long-tailed weasel and the ermine, or short-tailed weasel. Both of these species have black-tipped tails, but they are readily distinguished from each other by size. The long-tailed weasel is 14 – 18 inches long, weighs about five ounces, with a tail about half the length of the body. Short-tailed weasels are eightti ten inches long, weigh only 1 1/2 ounces with a tail less than one-third the length of their body. Typical of weasels, males are about 20 percent larger than females. Both species turn white in winter, except for the tip of the tail, and both species are brown in the summer; although the long-tailed weasel is yellowish to orange below, whereas the short-tailed weasel has a white belly.
The long-tailed weasel is distributed over all of Colorado although it seems to be most abundant in the mountains at moderate to high elevations; short-tailed weasels occur mostly in the mountains.
Long-tailed weasels live statewide in Colorado in most habitats, perhaps favoring brushy areas at the edge of forests where their rodent prey is most abundant. Short-tailed weasels mostly in mountain forests and meadows.
In addition to mice, weasels eat shrews, chipmunks, small ground squirrels, nestling rabbits and ground-nesting birds. They are quite capable of subduing animals larger than themselves, by wrapping their long body around the prey and killing it with a quick bite at the base of its skull. Although owls take a few weasels, no predator can afford to make a staple of another predator.
Weasels mate in the summer, a long delay in implantation of embryos, and gestation of about 30 days. Four to nine tiny young are born in April.
By David M. Armstrong Department of Ecology & Evolutionary Biology Environmental Studies Program, University Museum of Natural History University of Colorado-Boulder