Beavers are two primarily nocturnal, semi-aquatic species of rodent, one native to North America and one to Europe. They are known for building dams, canals, and lodges (homes). They are the second-largest rodent in the world (after the capybara). Their colonies create one or more dams to provide still, deep water to protect against predators, and to float food and building material. The North American population was 60-400 million, but as of 1988, 6-12 million, due to being hunted for fur, for their glands used as medicine and perfume, and because their harvesting of trees and flooding of waterways may interfere with other land uses.

General

Beavers are known for their natural trait of building dams in rivers and streams, and building their homes (known as beaver lodges) in the resulting pond. Beavers also build canals to float build materials that are difficult to haul over land. They use powerful front teeth to cut trees and plants that they use for building and for food.

They are known for their "danger signal": when startled or frightened, a swimming beaver will rapidly dive while forcefully slapping the water with its broad tail. This creates a loud "slap", audible over large distances above and below water. This noise serves as a warning to beavers in the area. Once a beaver has made this danger signal, nearby beavers dive and may not reemerge for some time. Beavers are slow on land, but good swimmers that can stay under water for as long as 15 minutes. (Wilson, 1971) Rarely, a frightened beaver attacks a human.

Beavers do not hybernate, but store sticks and logs underwater to feed on during the winter.

Fossil remains of beavers are found in the peat and other superficial deposits of England and the continent of Europe; while in the Pleistocene formations of England and Siberia occur remains of a giant extinct beaver, Trogontherium cuvieri, representing a genus by itself.

Beavers have webbed hind-feet, and a broad, scaly tail. They have poor eyesight, but keen senses of hearing, smell, and touch.

Beavers continue to grow throughout life. Adult specimens weighing over are not uncommon. Females are as large as or larger than males of the same age, which is uncommon among mammals.

Etymology

The word is descended from the Proto-Indo-European name of the animal, cf. Sanskrit babhru's, brown, the great ichneumon, Lat. fiber, Ger. Biber, Swed. bäver, Russ. bobr'; the root bhru has given "brown," and, through Romanic, "bronze" and "burnish."Encyclopedia Brittanica 11th Edn