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Beaver Notecard



Beaver (Castor canadensis)

Beavers are found throughout North America except the Southwest and Mexico. To beavers a pond is security… they are primarily aquatic. While swimming underwater, they have the ability to close their noses and ears as well as close a clear eyelid to protect their eyes from water and debris. The tail is perhaps the beavers’ defining characteristic; broad and flat with blackish scales, it serves as a rudder, sculling oar, and alarm-sounder when slapped on water. Two glands at the base of the tail contain castoreum, an oil that keeps the fur slick and waterproof. Like all rodents, they have large paired incisors that are always growing; beavers keep these trimmed by gnawing bark. Beavers typically weigh 40-60 pounds but some individuals may top 100 pounds.

Beavers build dams to slow water flow in streams and rivers, and they build a stable lodge for their shelter. Dams are well-engineered for water conditions. Lodges are made of sticks, mud, and rocks. Beavers primarily eat bark and cambium (the soft growing tissue under the bark of trees). Favorite trees include willows, maple, beech, birch, alder, and aspen. Cellulose, which normally cannot be digested by mammals, is a major component in their diet. Beavers have microorganisms in their digestive tract that help them to digest cellulose. Beavers form monogamous pairs and usually live in family groups of up to 8 related individuals called colonies. Younger siblings stay with parents for up to 2 years. Beavers are a “keystone” species as their dams create habitat for other aquatic organisms. As these engineers of the animal world build more dams they often come into conflict with human interests. From the point of view of water quality, water supply, and wildlife habitat, beavers are generally beneficial; beaver ponds slow the flow of water allowing sediment to deposit which clears the water, the pooling of water in the ponds aids groundwater recharge, and ponds provide valuable habitat for waterfowl and other animals. Dams also prevent flooding and soil erosion.

Beavers were pushed to the edge of extinction due to hunting and trapping. Their population made a remarkable comeback as farms were abandoned and beavers were protected. Beavers are the only animals other than humans that alter their environment to suit their needs. This distinction earned them the name “Little People” from the Native Americans of New England.

artwork and text by Steve Sierigk ©2001