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The Short-Tailed Weasel: Life Sped Up

Short-tailed weasel (Mustela erminea), summer phase
Steve Hillebrand (U.S.F.W.S.)
Short-tailed weasel (Mustela erminea), summer phase

While some animals get off comparatively easily in the winter by hibernating, or by gorging and then fasting, the short-tailed weasel has to hunt every day to keep its blast-furnace metabolism stoked. With a heart rate of several hundred beats a minute and little in the way of fat reserves on its long and slender body, the animal must consume half its body weight daily.

Nature has, however, given the weasel a few tricks for surviving the winter. The most obvious one is camouflage. As the snow falls, the short-tailed weasel trades in its brown and tan coat for a solid white one. Well, almost solid white; it retains a black tip on the end of its tail, which some researchers believe serves to distract predators from the animal’s body.

The same metabolism that keeps the weasel in an almost-constant state of hunger also makes it a quick, effective hunter. Aided by its keen sense of smell, the short-tailed weasel is capable of climbing trees, swimming rivers, diving into small rodent holes in the ground and hunting by day or by night in its search for prey. Its tastes are versatile, ranging from earthworms to waterfowl, although mice are its most common prey. In days of plenty, the energetic short-tailed weasel may kill more than it needs, and stockpile the carcasses for leaner days ahead.

Perhaps the most interesting adaptation of the short-tailed weasel is its reproductive strategy. With only a year and a half to live, the weasel doesn’t fool around when it comes to reproducing. Females become fertile at the tender age of six weeks and mate while still in the nest, sometimes even before their eyes are open. Adult females breed while still nursing their young. And in a clever and unusual twist, the fertilized eggs that result from the summer’s mating lie dormant inside the female for ten months; the eggs start growing again in the spring so that young are born in April or May, when there’s plenty of prey around with which to satisfy their voracious appetites.

"Field Notes" is produced by the Montana Natural History Center.

(Broadcast: "Field Notes,"  2/8/15, 12/17/19 and 12/20/19. Listen weekly on the radio Tuesdays and Fridays at 4:54 p.m., or via podcast.)

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