Perhaps no other rodent garners as much popular imagery as the beaver. Their avatars appear in Super Bowl beer ads as well as for toothpaste, construction companies, energy drinks, and even men’s work pants described as “tougher than a giant angry beaver.” An iconic bush plane is named for them, and they star in their own animated television show.
In Corvallis, Oregon, The Beavers represent the university athletic teams. Since 1958, Dillingham, a village in southwest Alaska, has hosted an annual cabin-fever-reliever festival, the Beaver Round-up.
Beavers in Alaska
Beavers are found throughout Alaska except for the extreme northern tundra, but in a likely response to climate change, they are expanding their range north. Using satellite imagery, researchers have documented an explosion of beaver on the Baldwin Peninsula near Kotzebue. In less than 20 years, the number of beaver dams counted there increased from two to nearly 100.
They are the second largest rodent, behind only the South American capybara. A large beaver weighs in at about 55 pounds, with some rare individuals tipping the scale at 100. Their russet-brown coat consists of a thick layer of long guard hairs underlain by a dense, soft underfur. The hind feet are large and webbed, excellent for swimming but clumsy on land. Their hairless, paddlelike tail is long and broad, useful for swimming and for balance on dry ground. A sharp tail slap on the water warns other beavers of danger. The scientific name, Castor canadensis, is derived from castor glands located at the base of the tail. These glands produce a pungent, oily substance, which beavers use both for scent marking and waterproofing their fur. Castoreum, collected from the glands, is used medicinally and in perfumes, as well as food flavoring in place of vanilla or raspberry. In Alaska, these animals are classified as furbearers and are sought for both their fur and excellent dark meat.
Beaver Dams
Few animals alter their habitat as much as beavers. Their dams are legendary feats of ingenuity. A record dam on the Jefferson River in Montana stretched over 2,100 feet long. Beavers use their impoundments, and related canals, for refuge from predators as well as to access the deciduous trees upon which they feed. Using its elongated orange incisors, a beaver can gnaw down a large tree in mere minutes. The largest beaver-cut tree measured 37 inches in diameter and 110 feet tall. The bark and upper branches of large trees are fed on in place; limbs and small trees are dragged and floated to the pond. Scientists say beaver ponds benefit a variety of fish and wildlife and promote plant diversity. Beavers sometimes draw the ire of people who lose trees, or find their property flooded in the wake of new dam construction. Highway workers wage battles with beavers that plug culverts and flood roadways.
The beaver lodge is a conical construction of mud, sticks, and grass that contains a living chamber above water level. Lodges are built in a pond, or on a bank, and accessed by underwater entrances, with at least one deep tunnel below the usual ice level. One lodge I measured was seven feet tall and arced for 42 feet, likely containing multiple chambers. The record lodge towered to 16 feet. Lodges usually support generations of beavers: dominant adults, yearlings, and young, called kits. Two-year-old beavers disperse to find food and establish their own colonies. Once local food sources are exhausted, a colony will abandon its lodge, individuals sometimes making overland treks to distant drainages seeking more abundant food sources.
Busy as a Beaver
Because many abandoned lodges dot the landscape, it can be difficult to census beavers. A “cache count” is one method biologists use to guesstimate the population. An active lodge is easily identified by the food cache frozen in front of it. Much as red squirrels amass spruce cones for winter use, beavers gather twigs and limbs into a cache constructed several feet in front of the lodge. The feed is anchored in the mud with the tops of the tallest sticks extending above water level. In winter, beavers swim under the ice, collect an item from the cache, and take it back to the chamber to feed. An inadequate cache means starvation. In years of extremely thick ice, beavers may freeze out and be unable to access their cache. In such famine conditions, beavers gnaw out of the lodge and go in search of food; bitter cold and predators claim many cast-outs.
The term “busy as a beaver” is well earned. Each year, just prior to freeze-up, in a flurry of activity, beavers gather their food supply. In late autumn 2019, a beaver colony in Denali’s Horseshoe Lake cut down a large number of aspens on a hilltop far above the lake and, beating freeze-up by mere days, succeeded in gathering their winter feed.
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