Urban ermine inspires weasel-related questions

While talking with two friends just inside a university entranceway, I saw a creature scampering in our direction just outside the glass doors. My first though was of a misdirected red squirrel running on the concrete. But this guy was longer, and bounded like a Slinky. A weasel!

We went outside and staked out the area, waiting for it to emerge from a crack between metal trim and the concrete. After a few minutes, it poked its head and torso from the 2-inch gap. Then it squeezed out, paused between us without fear and boinged past us to greenery.

Since then, I have heard of several more weasel sightings. Bob, who was there at the university, saw one in his woodpile a few days later.

Link Olson is not calling this the year of the weasel, but the curator of mammals at the University of Alaska Museum has gotten "a ton" of calls from people reporting lots of voles, including the easy-to-identify yellow-cheeked vole. An abundance of the weasel's frequent meal makes Olson think perhaps there might be a good population of weasels out there.

And who is this fierce little cylinder? The one I saw was an ermine, also known as a short-tailed weasel (a stoat in Europe).

There is something appealing about a weasel's sleek spunkiness that makes people want to keep one as a pet. Behind that cuteness is a killing machine. In the same family as wolverines and badgers, weasels are one of the busiest predators out there.

In the basement of the museum, Olson held up the jaw of a weasel that came to the collection from 15,000 feet on Denali. He showed how the weasel's jaw, unlike ours, is designed to move only up and down. The lower jaw is locked into the skull to strengthen the force of its bite.

"They have fewer molars than us," he said, noting that their all-meat diet does not require much grinding. "They've evolved to use their mouth to catch, kill, slice and swallow."

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

Polish researchers have studied "surplus killing" in weasels, in which weasels sometimes kill more voles than they can eat and cache them in the vole tunnels they commandeer. The scientists concluded that weasels did indeed go on killing sprees. But they found weasels did it more in cold temperatures, and in extreme cold temperatures they would harvest their caches more and hunt less. They wrote that rather than a "behavioral aberration," the weasel's excess vole killing was an adaptation to life in the far north.

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

"They can follow voles and pikas into really tight confines," he said. "But it's a trade off."

The weasel's long body leaves it more vulnerable to heat loss than animals like pikas, which are almost spherical. Weasels don't hibernate, so like their relative the wolverine they are always on the move.

"Weasels can't just hunker (to stay warm)," Olson said. "They have to be out hunting all the time."

Since the late 1970s, the University of Alaska Fairbanks' Geophysical Institute has provided this column free in cooperation with the UAF research community. Ned Rozell is a science writer for the Geophysical Institute.