The American beaver is nature's engineer, building dams in streams and rivers across Oregon.
Types of Beavers
The American beaver, the largest rodent in North America, commonly weighs in excess of 55 pounds. The beaver is highly modified for aquatic life with a compact body, paddle shaped tail, webbed hind feet, valves that close their ears and nose while diving, and a rich oil gland that waterproofs their fur. Under water, membranes cover the eyes.
Claws on the first and second toes are split and function in grooming; the ears and eyes are small; the tail is broad, scaly and nearly without hairs. The thick underfur is overlain with coarse guard hairs; overall, the pelage (coat) is dark brown dorsally (on its back) shading to a lighter brown ventrally (on its undersides). The tail and feet are blackish brown. There is a single annual molt.
In Oregon, the beaver occurs in suitable habitats throughout the state. It is almost always associated with riparian habitats bordered by a zone of trees, especially cottonwood and aspen, willow, alder and maple. Small streams with a constant flow of water that meander through relatively flat terrain in fertile valleys and are subject to being dammed seem especially productive of beavers.
They are powerful swimmers; propulsion is largely by use of the webbed hind feet and tail as the front feet are held close under the chin. The tail is also used to maneuver in the water. On land, the beaver is a clumsy waddler. Of all the beaver's behavioral characteristics, none is as legendary as its ability to cut trees for food or construction of dams and lodges. Beavers live in colonies composed of family groups usually consisting of a mated pair of adults, their yearlings, and their young-of-the-year, although occasionally groups may contain individuals over 24 months old other than the mated pair. Pairing is commonly considered monogamous and long term.
Beavers are most active in the evening or at night but they can sometimes be observed engaging in various activities at any hour. Beavers do not hibernate, although activity during winter may not be conspicuous because it is largely beneath the ice.
Photo by Kathy Munsel, ODFW