Mountain Beaver

Nature Notes by Dr. Frank Lang

In 1805, Chinook Indians showed Meriwether Lewis and William Clark a soft, brown fur robe made from the skins of a small mammal. Lewis noticed that none of the skins had tails and asked to see the animal. What he saw was a small, chunky, densely-furred mammal about the size and shape of a loaf of bread, blunt on both ends. The front? Equipped with long, stout whiskers, a pair of small, bright shiny eyes and small, round ears. The rear? A small, furred stump that passed for a tail and, in between, a muscular body with short legs and strongly clawed toes. Lewis and Clark called the animal “sewellel,” their version of the Chinook word for cloak or robe, “she-wal-lal.”

Later, early settlers called the animal mountain beaver. Other common names include boomer, whistler (it is said to have a quavering cry like the notes of a little owl), mountain rat, Chehalis, or North American short-tailed beaver. (It isn’t a beaver in spite of its common name.) Lewis thought it was a squirrel, a group to which it is most closely related. Today we consider the mountain beaver, or Aplodontia rufa to use its scientific name, the only surviving member of the most primitive family of rodents with a fossil history dating from the Upper Eocene about 50 million years ago. Aplodontia is found nowhere in the world except the wet climate areas west of the Cascade Mountains from southern British Columbia to northwest California and the Sierra Nevada.

Mountain beaver live in shallow burrows that they dig in soft, moist soils of gulches and ravines. Burrows radiate out from nests and frequently water trickles down the runways. Mountain beaver cannot concentrate their urine and require a high daily water intake, which may explain their preference for wet burrows and vegetation of high water content. I’ll bet they just love our so-called wintery spring this year.

A single mountain beaver occupies each nest. Home ranges overlap and runways are shared. Although they venture forth to forage mainly at night, you might get a glimpse of them in the early morning or at dusk. They do not hibernate.

Mountain beaver harvest vegetation which they bring back to burrow entrances to line their nests, or store to eat. They collect whatever plants are in their territory. Unfortunately, the little beasts include important timber species among their gatherings. The most frequent damage is to newly-planted seedlings in plantations. The timber industry wages a trapping war where mountain beaver damage is a problem.

In our area the mountain beaver lives at higher elevations. To find colonies drive up Tolman Creek Road south of Ashland to above 4,000 feet, and walk around in wet meadows or go to Bear Camp Pasture on the Galice to Agness Road west of Grants Pass and walk uphill near the outhouse. Look for piles of fresh cut vegetation or fresh soil tailings at burrow entrances for evidence of activity. If you aren’t careful you might discover, as I often have, how they might have gotten the common name of mountain boomer. When you suddenly step through their shallow burrows on steep hillsides, you fall down and go boomer.

— Dr. Frank Lang   

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