American Beaver

Castor canadensis

Description

American beavers are the largest rodents in North America. This animal has a waterproof, glossy, reddish-brown or blackish-brown fur; the under-hairs of this fur are very fine and protected by thicker guard-hairs. Beavers have a large head with very large, orange colored incisors (teeth) used for cutting hard wood; these incisors will continue to grow throughout the beaver’s life. The backend of a beaver is shorter than the front end while walking because their front legs are shorter than the hind legs. As a primarily an aquatic species, beavers have short rounded ears and nostrils that can be closed while swimming. They also have a transparent membrane on their eye to help them see while swimming under water. A beaver’s tail is broad and flat with the appearance of blackish scales.

Habitat

The American beaver can be found throughout all of North America, except northern regions of Canada and the deserts of southern United States and Mexico. This animal builds an oven-shaped lodge it woven together with sticks, grass and plastered with mud. These lodges can typically be found on islands, banks of ponds and shores of lakes very close to the water’s edge or even partly hanging over. The central room inside the lodge is about 8 feet wide and 3 feet high with a blanket of bark, grass and wood chips covering the ground. Over time beavers repair, elaborate and expand their lodge. The lodge has a central chamber located inland and slightly above water level with two entrances, one entrance opens to the center of the hut floor while the other goes directly into water. Beavers also build dams, these are used to slow down the flow of water and are carefully engineered; dams in slow water are built straight but dams in fast water are built curved so it will not be washed away.

Feeding Behavior and Diet

The diet of this animal consists of bark and cambium (soft tree tissue beneath bark) of willow, maple, poplar, beech, birth, alder, and aspen trees. Vegetation (such as water vegetation, buds, and roots) can also be consumed because beavers have microorganisms in a sac between the large and small intestine called a secum. Beavers will travel great distances from their homes to find food. If an abundant food source is found further away, beavers build canals so they can float food back to their lodges and save the energy of carrying food. This species will store logs and twigs under water to preserve it for winter feeding.

Reproduction

American beavers are monogamous mammals, only seeking another mate if the current mate has died. Northern populations of this species breed between January and March, while southern populations breed during late November or December. A litter of 1-4 kits are born between April and July, about 3 months after mating. Both male and female beavers play parental roles in rearing young. Newborn kits (young beavers) have full fur coats, open eyes, and can swim after 24 hours. Within a few days of birth kits leave the lodge with parental guidance to explore their surroundings. Kits nurse from their mother until they are weaned between 14-90 days after birth. Kits remain with their parents for about 2 years before leaving to create their own colony several kilometers away. Beavers do not reach sexual maturity until their third year and produce one litter of kits per year.

Months and Times of Activity

This species is mostly nocturnal but can be occasionally seen during the day (around dusk).

Special Features, Stories, Relationships

• Beavers are very territorial and will mark their territory using musk-like secretions of castoreum, produced by large anal (3.4 by 2.2 in) and castor glands (3.0 by 1.0 in) located at the base of the tail. These secretions are deposited on mud piles that have been placed around the parameter of the territory.
• Beavers live in colonies of up to 8 related individuals.
• Beavers warn other animals of danger by creating a powerful noise, slapping their tails against the water. Many other species within the area rely on these warnings made by beavers.
• To read legends featuring this animal go to: http://www.firstpeople.us/FP-Html-Legends/HowTheBeaverGotHisTail-Ojibwa.html
• Children’s book featuring this animal: Little Beaver and The Echo by Amy MacDonald

References

Anderson, R. 2002. "Castor canadensis" (On-line), Animal Diversity Web. Accessed November 03, 2014 at http://animaldiversity.ummz.umich.edu/accounts/Castor_canadensis/