Weasels: Tiny but mighty

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Imagine a chipmunk weighing 3 ounces sound asleep in a small chamber about 24 inches below ground.

The den is lined with finely chewed leaves. It’s safe and secure…until a least weasel, the smallest carnivore in North America (less than two ounces), explores the tunnel leading to the den.

Trimmer than a chipmunk, the weasel easily navigates the chipmunk’s tunnel. The chipmunk’s life ends quickly.

The tiny killing machine grabs the chippy, and immediately bites down on the base of its skull.

The weasel devours the brain, internal organs and major muscles. Then it’s off to its next victim.

Prey

Least weasels are killing and eating machines. A chipmunk will sate its appetite for most of the day, but most meals consist of smaller prey such as mice and voles.

If small mammals know fear, weasels must instill terror.

Least weasels specialize in small prey. Ermine, or short-tailed weasels, which weigh up to 3.5 ounces, take shrews, voles, birds, and young rabbits.

And long-tailed weasels, weighing in at 3 to 11 ounces, take cottontails, squirrels, and assorted smaller mammals.

Weasels minimize competition for food by eating different sized prey. Least weasels take the smallest prey, ermine specialize on mid-sized prey, and long-tailed weasels take the largest prey.

Furthermore, within each weasel species, males are larger than females.

So males of each species can take bigger prey than females, thus further reducing competition for food.

Traits

Weasels’ long, slender bodies allow them to enter underground burrows in search of prey.

No subterranean burrow is truly safe. Even mice, shrews, moles, and voles are at risk.

Above ground, rabbits, squirrels, small snakes, lizards, frogs, birds and their eggs, and larger insects round out the weasels’ diets.

Despite the ferocity and efficiency of weasels’ eating habits, they, too, are links in the food chain.

Snakes, owls, hawks, foxes, coyotes and cats do their best to ensure that what goes around comes around.

Though seldom seen by people, weasels are common and widespread.

Long-tailed weasels are the largest and most widely distributed of these three common North American species. They measure up to 17 inches long, including tail.

Ermine, or short-tailed weasels, grow to about 11 inches in length. And least weasels, despite measuring just seven to eight inches in length, are perhaps the most ferocious of the group.

Camouflage

During the spring and summer, weasels are brown above and white below.

But in October, as days get shorter, weasels molt into an almost pure white pelage that creates a perfect camouflage when the snow flies.

In the southern part of their range, where snow is less common, long-tail weasels retain their brown fur all year long.

Though most active between dusk and dawn, weasels hunt any time they’re hungry. Their small size and secretive nature, however, make them difficult to observe.

They spend much of their time exploring the grassy runways of meadow voles and underground burrows of deer mice and chipmunks.

During winter, they often tunnel beneath the snow. Out of sight, out of mind — except for potential victims.

Breeding

Unlike many small mammals, weasels employ unusual reproductive strategies. Least weasels can breed at any time of year, even in mid-winter.

If food is abundant, they take advantage of the situation and make more weasels. Two to three litters per year are typical.

Gestation lasts about 36 days, and litter size averages five.

Ermine and long-tailed weasels bear a single litter of five to eight young each year.

These two species mate in mid-summer, but the tiny embryos do not implant on the female’s uterine wall until sometime in the spring.

This “delayed implantation” allows males and females to complete the energetically demanding task of mating when food is abundant rather than waiting until spring when food is often in short supply.

Weasels’ claim to fame as efficient killing machines hardly endear them to many nature watchers, but without them, we might live in a world overrun with rodents.

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Scott Shalaway, who holds a Ph.D. in wildlife ecology from Michigan State University, writes from his home in rural West Virginia. A former faculty member at Oklahoma State University and the University of Oklahoma Biological Station, he has been writing a weekly nature column for newspapers and freelancing for magazines since 1986. He can be heard on Birds & Nature from 3-4 p.m. Sunday afternoons on 620 KHB Radio, Pittsburgh, or live online anywhere at www.khbradio.com, or on the Tune-In radio app. Visit his website at www.drshalaway.com or contact him directly at sshalaway@aol.com or 2222 Fish Ridge Road, Cameron, WV 26033.

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