Life Tracks
Wisconsin Dept. of Natural Resources - Bureau of Wildlife Management - Dec. 1983 - PUBL-WM-0593 83REV

The Beaver
(Castor canadensis)

By Charles M. Pils - Furbearer Specialist



Description

The beaver is the largest rodent in North America. Adults are from 35 to 46 inches long including a flattened 12- to 18-inch tail. The wide flat tail is covered with leathery scales and sparse, coarse hair. It can be used as a rudder while swimming and as a support on land. The hind feet are very large and contain 5 long webbed toes. Front feet are small and dextrous, which allows the beaver to carry a variety of objects such as stones and sticks for construction of dams. The guard hair is long and coarse and ranges in color from pale yellow to black. The most common pelts are colored reddish-brown. Beavers have large, sharp, front teeth, small ears and nostrils that can be closed for swimming beneath the surface. Adults weigh from 45 to 60 pounds, although the heaviest Wisconsin beaver ever recorded weighed 110 pounds and was caught in Iron County.


Reproduction:

Most beavers become sexually mature during their 2nd year. Wisconsin beavers breed from late January to late February; fetuses develop for 120 days until they are born. The average litter size is 4 kits and ranges from 1-8. Beavers mate for life and protect the kits until the young are 2 years old. The kits are then driven off to find their own territories.


Food:

Beavers eat the leaves, twigs and bark of most species of woody plants which grow near water. Aspens, poplars, alders or willows are usually preferred. These large rodents also rely on sedges, water grasses, fleshy roots and water lilies as food. Beavers prefer small trees, but will feed on larger trees. During the fall, beavers cache their food supply of branches and logs in the water, near a lodge or bank burrow. Materials from the cache are eaten during the winter, although beavers will continue to go ashore to cut fresh trees as long as they can break through the ice at the edge of their pond.


Habits and Habitats:

Beavers are the only wildlife in Wisconsin that actually change their environment to suit their needs. Small streams are dammed by beavers which results in construction of a pond. In the pond is the lodge and winter food cache. Surrounding the pond are canals and runways that the beaver uses to transport building materials and food to the pond. The dam and lodge are constructed of sticks and mud, which results in a strong, durable coating for their house. The result of this extensive engineering is wide-spread flooding of woodlands arid agricultural land. Wildlife species such as otter, mink, muskrats, deer, bear, waterfowl, waterbirds and grouse benefit from creation of flooded "edges." On the other hand, beaver dams cause trout streams to become silted and warmed. Dams prevent trout migration and result in a lowered trout population. Beavers cause numerous complaints by plugging road culverts and flooding roads, railroad tracks and agricultural fields.

Beaver homes consist of lodges, about 15 feet in diameter and 5-6 feet high, (Fig. 1), or burrows in stream banks. Lodges consist of one or more compartments which may be occupied by one or more family groups. Each compartment has two openings, both underwater, for exit or entry.

The major wildlife predators of adult beavers are coyotes, wolves and bears. Otter and mink may occasionally prey on kits.

Tularemia, a disease spread directly by water or the tick, has been recorded during the 1950's and was confirmed in north central Wisconsin during 1981.


History in Wisconsin

Beaver were abundant in Wisconsin before settlement, yet the beaver dramatically decreased to the point of extinction by 1900 as a result of extensive logging and fur trapping. The present increase in beaver numbers is primarily a result of beaver adaptability, a lack of natural predation, restocking, and the regrowth of aspen forests. During the last decade, relatively low pelt prices have prompted lower trapping pressure and low harvests. The net result of all these factors has been a large increase in beaver densities in several habitats near streams, lakes or ponds.

The range of the beaver in Wisconsin extends throughout the state. The entire northern half of Wisconsin now has very high beaver populations. Only agricultural areas lacking suitable aquatic habitat found in eastern and southeastern Wisconsin contain low densities of beaver.


Management

Throughout the last 90 years, beaver management has evolved from complete protection of a nearly extirpated furbearer to the implementation of liberal trapping seasons and subsidized trapping contracts.

Wisconsin beaver trapping seasons have fluctuated from a year-round season that began in 1850 to 6 periods (1893-1947) in which seasons were closed from 1 to 14 years. These closed seasons plus the program of live-trapping and restocking were instrumental in replenishing Wisconsin's depleted beaver population.

Mandatory beaver registration was initiated in 1934 in order to maintain an accurate count of the beaver harvest, which has varied from a low of 1,869 in 1935 to a high of 29,447 in 1979-80. Skinned and stretched pelts were also required to be registered and tagged in order to check for possible illegal methods of harvest, namely shooting or spearing. Beaver registration was removed in 1983-84 primarily because of the initiation of the fur trapping questionnaire in Wisconsin. This questionnaire gave wildlife managers the same basic harvest information while saving the Department considerable time and money.

During the past 13 seasons, $4.2 million worth of pelts have been trapped in Wisconsin, making the beaver one of the most economically valuable furbearers in the state. Beaver trapping has also provided considerable recreational opportunity for Wisconsin residents. Therefore, any management recommendations should consider the quantity and quality of wildlife habitat created, impacts on flooded areas, beaver-trout interactions, the value of pelts, recreation time provided, and monetary incentives provided by trappers to the Wisconsin economy.

The current beaver management program is based on extremely high statewide populations, which have increased damage problems to a high level. A long, liberal trapping season with no bag limits is the primary tool used to control beaver numbers. Subsidized contracts, which allow beavers to be trapped at specified areas for a fee, started in 1983. Current beaver trapping regulations are structured to minimize the incidental harvest of otter.


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