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The Mammals of Texas - Online Edition

American Beaver
Order Rodentia : Family Castoridae : Castor canadensis Kuhl

American Beaver (Castor canadensis).  Photo by John L. Tveten.Description. A large, robust, aquatic rodent with a broad, horizontally flattened, scaly tail; hind feet webbed; upperparts in fresh fall pelage dark, rich, chestnut brown which fades by spring; underparts paler, often with silvery sheen. Sexes colored alike. External measurements average: total length, 1,160 mm; tail, 400 mm; hind foot, 178 mm. Weight, averages 18 kg; rarely as much as 27 kg. The dental formula is I 1/1, C 0/0, Pm 1/1, M 3/3 X 2 = 20.

Species distribution mapDistribution in Texas. Found over most of the state where suitable aquatic habitat prevails; absent from the Llano Estacado and some adjacent areas and from much of the Trans-Pecos.

Habits. Beavers are essentially aquatic and require water in the form of a pond, stream, lake, or river for their well-being. Because of their skills in regulating water level and stream flow with dams, beavers are able to convert an otherwise unfavorable area into one that is habitable. But they must be ever alert as water engineers because their ponds tend to fill up with sediment washed off the slopes above and in time become meadows, forcing the beavers to move to new sites. Large rivers and lakes offer suitable habitat in places where natural food and den or house sites are available, but the largest populations are on small bodies of water.

In cold regions, beavers live in houses constructed of sticks and mud and enter and leave them by means of underwater tunnels or "plunge holes"; in Texas they may burrow into cut banks of streams or lakes. Burrows examined in the Rio Grande in the Big Bend section of Texas were large enough to admit a man and were 10 m or more in length. Burrows as long as 50 m have been reported. Burrows, or houses, are used for loafing, sleeping, and rearing the young.

The average beaver colony consists of six or seven animals, usually including parents and their young of two age classes; rarely is it as large as 12.

Beavers feed on a variety of vegetation, but the inner bark of willows and cottonwood seems to be their mainstay. In summer a number of herbaceous aquatic plants and sedges are eaten. In central Texas, where willows are absent, beavers in winter utilize as first choice such trees as button willow, juniper, and pecan and rely heavily on Bermuda grass, beard grass, ragweed, and yellow water lily in summer. Thus, the plants eaten and their order of preference depend in large measure on availability.

Breeding begins in January or February, and the young are normally born in May or June after a gestation period of about 107 days. Beavers are usually monogamous, and normally only one litter of three to four young is produced each year, but some females produce a second litter in August or September.

At birth the kits are fully furred, the eyes are open, and the incisor teeth are visible; they weigh about 450 g. The tail is broad and flat, as in adults. They grow rather slowly and attain a weight of about 10 kg the first year. They mature sexually the second year. Rarely, yearling females may breed and produce young. The young often stay with the family group through the second year.

Because of the high commercial value of their pelts, beavers figured importantly in the early exploration and settlement of western North America. Thousands of their pelts were harvested annually, and it was not many years before beavers were either exterminated entirely or reduced to very low populations over a considerable part of their former range. By 1910 their populations were so low everywhere in the United States that strict regulation of the harvest or complete protection became imperative. In the 1930s live trapping and restocking of depleted areas became a widespread practice which, when coupled with adequate protection, has made it possible for the animals to make a spectacular comeback in many sections. Their value as soil and water conservationists is well-known and, in most sections of the country, appreciated. They can be destructive to crops, trees, and irrigation systems, however, in which case they can be live-trapped and removed from the area.

Photo credit: John L. Tveten.