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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