Catching a glimpse of a weasel in winter always involves a bit of luck. Weasels are the only members of the Mustelidae family that turn white in winter, so they are well camouflaged against the snow. What’s more, like the mice and voles that are their primary prey, they spend much of their time under the snow, following their noses through the twilight world of tunnels cleared by squirrels, mice, weasels, and other small North Country mammals that rely on a healthy snowpack during the cold months.
Weasels are the smallest members of the Mustelidae (weasel) family, which includes mink, pine martens, fisher, otter, badgers, ferrets, and even wolverines. They’re all remarkably effective predators with long bodies, short legs, and a ferocious temperament. In winter, they will consume about 30 percent of their body weight daily in order to survive.
In Minnesota, we have a healthy representation of mustelids, including three distinct species of weasels, the least weasel, the short-tailed weasel, and the long-tailed weasel. The recent visitor to our backyard, pictured here, was a short-tailed weasel that was attracted to the remains of a deer rib cage after it was boned out for the venison.
The remaining scraps still stuck to the bones regularly attract a long list of birds, but also bring in the occasional marten, fisher, or weasel.
This particular weasel was skittish, which isn’t unusual for these small predators. While they are formidable if you’re a mouse, they can also be prey for larger predators, ranging from mink to hawks. Their white pelage in winter helps disguise them from prey but also helps keep them from falling prey. The only exception to their white fur is a bit of black at the tip of their tail.
With spring gradually making its way to the North Country, the female weasels could soon be having their young. Weasels actually mate in the late summer or fall, but the embryos only develop for a couple weeks before going into a kind of suspended animation. In late winter or early spring, the embryos finally implant in the uterus and develop for another month or so before birth. This is an unusual reproductive strategy, known as delayed implantation, which is found in about two percent of mammals, including bears in addition to mustelids.
Most biologists believe that delayed implantation helps to ensure that young mammals are born at the time of year when they are most likely to survive.
I’ll be watching for a few more glimpses of our neighborhood weasel over the next few weeks as it negotiates another challenging period, the transition from winter white to summer brown. For potential prey like a weasel, timing that change to the disappearance of the snow is critical. If they don’t get it right, they can be awfully vulnerable out there.