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Living with Beavers

Ecology

Beavers are found throughout North America, except for the arctic tundra, most of peninsular Florida, and the southwestern desert areas. Local abundance may occur wherever aquatic habitats are found. Populations are limited by habitat availability, and the density will not exceed one colony per ½ mile under the best of conditions.

Beaver fur consists of long, coarse outer hairs and short, fine inner hairs. The fur can range in color, but is most of dark brown. Scent glands secrete an oily substance called castoreum, which the beaver uses to waterproof its fur. Beavers are territorial and mark their territory by creating small mounds of mud, leaves, and sticks, and which they coat with castoreum. More susceptible to predators on land, beavers tend to remain in the water as much as possible. They are excellent swimmers, and with valvular nose and ears and lips that close behind the four large incisors teeth, they are able to remain submerged for up to 15 minutes. The flat, scaly tail stores fat, and is used to signal danger by slapping the surface of the water.

Habitat

Photo of beaver in water.

Beaver habitat is almost anywhere there is a year-round source of water, such as streams, lakes, farm ponds, swamps, wetland areas, roadside ditches, drainage ditches, canals, mine pits, oxbows, railroad rights-of-way, drains from sewage disposal ponds, and below natural springs or artesian wells. Beavers select habitat with accessible foods, available lodge or denning sites, and usually associated suitable dam sites. They often then modify habitat to their needs by building dens and dams and creating ponds.

Dams and Other Activity

Beavers build dams to create deep water for protection from predators, for access to their food supply and to provide underwater entrances to their dens and lodges. Dams are constructed and maintained with whatever materials are available to the beaver near the water’s edge. Examples of dam building materials used range from wood, plant parts, fencing materials, bridge planking, rocks, mud, wire and other metal, sagebrush, cornstalks, plastic, and other materials. The sound of flowing water stimulates beavers to build dams or to repair leaks in them. However, they routinely let a leak in a dam flow freely, especially during times of high waters. Leaking, often derelict, dams are common in active colony sites during the summer months when beaver are not reliant on water to store cached food and are not inhibited by ice in pursuit of fresh near or above the water’s edge.

Beavers keep their dams in good repair and will constantly maintain the dams especially during times of the year when drops in water levels could compromise the security of the dens and lodges or access to cached food. Typically, beaver colonies will build and maintain more than one dam to impound sufficient water for year-round habitat of an area. In cold areas, dam maintenance is critical because dams must be of sufficient height to ensure water depth sufficient to ensure that the impounded water does not freeze to the bottom, which would prevent access to cached food and potentially trap beaver in their lodges or bank dens.

Photo of wetlands created by beaver activity.

Beaver dams create and maintain wetland habitat.

Forage sites are areas where beavers cut trees, shrubs, cattail, bulrush, and other vegetation both for food and building materials. There will be a pile of wood chips on the ground around the base of recently felled trees. Limbs that are too large to be dragged by beaver are typically stripped of bark over the course of several days. Branches and twigs under ¾-inch in diameter are sometimes eaten entirely. Because of this sometimes heavy consumption of the woody parts of the branches, the floor of beaver ponds may be covered with thousands of beaver droppings that are essentially sawdust pellets.

Slides are the paths where beavers enter and leave the water, typically on a bank where their walking and dragging of cut materials creates a trough or “slide.” They are 15- to 20-inches wide, perpendicular to the shoreline and have a slicked down or muddy appearance. In fall, actively used slides will have ice formation in them when temperatures fall below freezing during the night when beaver are most active in cutting and dragging limbs, branches, and twigs. Beavers also construct channels leading to their ponds, which are used to float food—such as small, trimmed trees—from forage sites. With receding water levels during summer, beaver activity shifts toward building and maintaining canals to access new food supplies.