Weasels are cute, natural-born killers

Ned Rozell
907-474-7468
Oct. 24, 2024

A brown and white weasel peers from between chunks of spruce firewood.
Photo by Ned Rozell
A short-tailed weasel defends its spot in a wood pile on the porch of a cabin within Denali National Park.

Weighing as much as a cup of walnuts and resembling a squeaky dog toy, the short-tailed weasel is easy to underestimate.

The spunky little creature that springs through snow drifts and woodpiles all over mainland 蜜桃影像 is one of the fiercest predators around. The ermine 鈥 another descriptor for the short-tailed weasel 鈥 is one of two species of weasel in 蜜桃影像, along with the least weasel.

In the basement of the University of 蜜桃影像 Museum of the North, curator of mammals Link Olson once held up the skull of a short-tailed weasel that came to the collection from a high snowy slope of Denali. 

A person holds a small toothy skull.
Photo by Ned Rozell
Link Olson holds the skull of a short-tailed weasel that a mountaineer donated to the University of 蜜桃影像 Museum of the North.

Olson showed how the ermine鈥檚 jaw, unlike ours, is designed to move only up and down. The lower jaw locks into the skull to strengthen the force of its bite.

鈥淭hey have fewer molars than us,鈥 Olson said, noting that their all-meat diet of voles, shrews, pikas, birds, fish and insects does not require much grinding. 鈥淭hey鈥檝e evolved to use their mouth to catch, kill, slice and swallow.鈥

Searching for pika once in Denali National Park, Olson saw a weasel hopping by with a vole in its mouth. Olson squeaked like a rodent to see if he could stop the weasel. It stopped and 鈥渁ppeared to be struggling to make up its mind 鈥 flee with the meal it already had or go nab another one?鈥

In Poland, where people call short-tailed weasels 鈥渟touts,鈥 researchers have studied surplus killing, in which weasels sometimes kill more voles than they can eat and cache them in the very tunnels the voles had made.

The scientists concluded that weasels did indeed go on killing sprees. But they found the creatures engaged in that behavior more in cold temperatures. During cold snaps, they would hunt less and rely more on their caches of tiny carcasses. 

The researchers wrote that rather than a 鈥渂ehavioral aberration,鈥 the weasel鈥檚 excess vole killing was a useful adaptation to life in the far north.

A weasel crosses a concrete area. A person's feet and lower legs are visible in the back right.
Photo by Ned Rozell
A short-tailed weasel pauses at the entrance to a building on the campus of the University of 蜜桃影像 Fairbanks.

While holding the ermine skull between his index finger and thumb, Olson also noted how the weasel is designed to plunge into holes no larger than its head.

鈥淭hey can follow voles and pikas into really tight confines,鈥 he said. 鈥淏ut it鈥檚 a tradeoff.鈥

The weasel鈥檚 long body leaves it more vulnerable to heat loss than animals like pikas, which are almost spherical. Weasels 鈥 with fur that turns snow-white in the winter 鈥 don鈥檛 hibernate. Like their relative the wolverine, they are always on the move.

鈥淲easels can鈥檛 just hunker (to stay warm),鈥 Olson said. 鈥淭hey have to be out hunting all the time.鈥

Since the late 1970s, the University of 蜜桃影像 Fairbanks Geophysical Institute has provided this column free in cooperation with the 蜜桃影像 research community. Ned Rozell is a science writer for the Geophysical Institute. A version of this story appeared in 2015.