Castor canadensis
Castor canadensis
"Identification: Head and body 25-30in. (63-76cm); tail 9-10in. (23-35cm); wt. 30-60lbs. (13.5-27kg). A stick-and-mud dam across a stream, or a large conical house of similar material at the edge of a lake and stumps of small trees in the vicinity showing tooth marks will reveal the presence of the Beaver. A loud report, caused by the tail as the Beaver dives below the surface of the water, will also indicate its presence. Rich brown in color; tail naked, scaly, shaped like a paddle, flat, about 6in. (15cm) wide. Huge front teeth chestnut-colored on front faces; hind feet webbed, 2nd claw double. Skull...has 20 teeth. There are 4 mammae."(1)
"The beaver was made for the water. Its large, chunky body, dense waterproof fur, and subcutaneous layer of fat minimize heat loss to icy water. A transparent eyelid protects the eyes, and the ear and nose openings can be closed while the animal is underwater. Adaptations of the respiratory and circulatory systems increase their efficiency. Large, webbed feet and powerful hind legs further enhance its underwater abilities."(3)
"In lowland areas, where they occur along rivers and drainage canals, beavers may give up houses in favor of bank burrows which they dig."(4)
"Beavers are exclusively vegetarian in diet. A favorite food item is the cambial, or growing, layer of tissue just under the bark of shrubs and trees. Many of the trees that are cut are stripped of bark on the spot, or carried to the pond for storage under water as a winter food cache. Buds and roots are also consumed, and when they are needed, a variety of plant species are accepted. There are definite preferences, however, and aspen and willow are high on the beaver's list of favorites. The animals may travel some distance from water to secure food. When a rich food source is exploited, canals may be dug from the pond to the pasture to facilitate the transportatioon of the items to the beavers' homes....
Much of the food ingested by a beaver consists of cellulose, which is normally indigestible by mammals. However, these animals have colonies of microorganisms living in the cecum, a pouch between the large and small intestine, and these symbionts digest up to 30 percent of the cellulose that the beaver takes in. An additional recycling of plant food occurs when certain fecal pellets are eaten and run through the digestive process a second time."(4)
Young: Born April-July; usually 2-4, occasionally 8; gestation period about 128 days; 1 litter a year. Kits furred and with eyes open." (1)
"The social unit in beaver life, known as a colony, consists of four to eight related individuals, probably dominated by an adult female, although in some cases a male may be dominant. Once a year, the mature female produces several young, known as kits, after a gestation of about 107 days. The kits are born fully furred with the eyes partially open, and the incisor teeth erupted. Accounts as to duration of dependency on the mother suggest a period of six weeks to three months. The animals may continue to grow for several years; they become sexually mature in their second year. There is some evidence that the presence of a mature female in a colony inhibits sexual maturity in younger females in the group. Much evidence suggests that the dominant male and female animal in a colony form a monogamous pair."(4)
Economic Status: An important fur animal and water conservationist; timber destroyed is mostly low-grade; occasionally floods roads or fields; meat edible. Exterminated in much of former range, now being reintroduced widely. May be seen in Natl. Parks in Canada; Glacier, Yellowstone, Grand Teton, Mt Ranier, Olympic, and Rocky Mt. Natl. Parks in U.S."(1)
"One of the few animals besides man that modifies its environment to any great degree, beaver build dams of sticks and mud across streams and slow rivers. After felling trees along the banks, cutting them into small sections and eating the bark, the stripped sticks are woven into the dam and held in place with mud. They also build large cone-shaped lodges, either in deep water or near the bank. The entrance is underwater but the nest chamber is well above the waterline."(3)
The Beaver's Lodge
"The life of the colony is centered on the lodge and pond.
The pond itself has profound ecological effects on the surrounding habitat. The flooding causes the deaths of some trees. The dead trees in turn, provide shelter for various birds that otherwise would not inhabit the place. Water-loving plants thrive in and around the pond, and these provide food and shelter for a variety of animals. The retention of water in the pond causes the local water table to rise, enhancing the growth of additional vegetation. The pond and surrounding wet area acts as a reservoir, preventing rapid runoff of water during rains and ensuing that the stream flows steadily throughout the year. The predictable stream flow allows trout to survive, and further downstream, it allows humans to plan agricultural activities. When the pond fills with silt it becomes less useful to the beavers, and eventually the colony may abandon the site and move further up or down stream. The abandoned pond gradually becomes covered with meadow grasses, and the resulting lush open area is productive of protein-rich grasses for cattle and horses. This typical beaver meadow, a distinctive feature of the northern mountains, if referred to in Spanish as a vega.
in the early days of American exploration of the Rocky Mountains, the trapping of beaver fur was a principal economic lure. So easy are beaver to locate and trap that by approximately 1900 the animals were largely extirpated from much of the West, including most New Mexican mountain ranges. When beaver are gone the dams fall into disrepair, the ponds disappear, and the water table falls. Stream and pondside vegetation dies, and the animals that depend on that habitat leave or become extinct. The vegas are no longer good grazing land, and the area looses its value for man. The summer rains, unchecked by the dams, cut deeply into the soil and wash it away. Soon, instead of a fertile riparian community, the streamsides are rock-strewn arroyos that hold water only during occasional floods. Downstream, the farmers leave, now that their irrigation water is a thing of the past. The effect of the uncontrolled commercial exploitation of beaver was a classic example of the public and environmental cost of private enterprise. Because the beavers are so obviously beneficial, they were wisely reintroduced to most of the suitable habitats throughout the state and are now widespread."(4)
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Page Last Modified December 30, 1999
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