Beavers: Castoridae

Physical characteristics: Also commonly called simply the American beaver, the North American beaver weighs from 33 to 75 pounds (15 to 35 kilograms). They have yellowish brown to black fur.

Geographic range: North American beavers are found in Alaska, Canada, throughout the continental United States, and the extreme northern areas of Mexico. These animals are not found in desert regions or southern Florida. They have also been introduced in Finland, Russia, and Argentina.

Habitat: Like all beavers, the North American beaver is aquatic and lives near water in the form of a pond, stream, lake, or river.

Diet: North American beavers eat a variety of plant material. They prefer the cambium, the soft layer between the wood and bark, and leaves of trees such as aspen, birch, aspen, willow, cottonwood, and alder. Their diet also can include aquatic plants, such as pond weeds, water-lilies, and cattails. North American beavers also eat grasses, shrubs, and herbs.

North American beavers eat mostly cellulose, which is broken down by microorganisms in their cecum (SEE-kum), a part of the digestive system. (© Phil Schermeister/Corbis. Reproduced by permission.)

Behavior and reproduction: North American beavers build more extensive dams that alter the landscape than their European counterparts. They are primarily nocturnal but are also frequently active during the day. As the weather gets cooler, beavers stockpile food for the winter by storing it underwater in their lodge or den. When they are able to break through the winter ice, these animals continue to cut down trees. In the northern areas, this underwater food storage may be the beaver's main food supply for months. In the southern areas, beavers are more active year around.

North American beavers and people: North American beavers are part of Native American myths. An Apache myth says that beavers have the magic of the medicine men. Beavers have played an integral role in the development of the United States and Canada. These animals were highly valued for the pelts. The beaver pelt became a unit of currency in colonial times, often leading to fights over trapping territories. The potential for profit, money, encouraged trappers to continue to move west, and settlers soon followed the trappers. Beavers were hunted so intensively throughout North America that the population was reduced by 90 percent by the late twentieth century.

Altering its environment with dams and the creation of ponds benefits the beaver's ecosystem. The ponds help control runoff and help the fish and other organisms flourish. There are over fifty species of animals that live in beaver ponds. The damming of streams raises the level of the water. This causes the tree species that cannot survive in permanently wet soil to die, allowing for the spread of other species. Some people consider these animals a pest. The cutting of trees can damage crops and timber. Their creation of dams can cause flooding that can also harm woodlands and farms.

Conservation status: The IUCN does not list the North American beaver as a threatened species. ∎