Beaver (Castor canadensis)
The beaver is the largest rodent in North America, the adult reaching 4 1/2 feet (1,371 mm) long and weighing up to 90 pounds (40.8 kg). Its common name is derived from the Anglo-Saxon word beofor.
Description
Beavers are easily distinguished by their large size, webbed hind feet and large horizontally flattened tail. The body fur is dark brown above and lighter brown below; the tail is blackish.
Distribution and abundance
Originally, the range of this species included most of North America, but as a result of extensive trapping and other byproducts of civilization, most of the beavers were exterminated in the eastern and southern portions of this range. In Missouri, beavers were common in every major watershed prior to the Civil War, but by 1875, the population had started to dwindle. By 1895 only a few colonies remained, and these were primarily along the Missouri River in north-western Missouri and possibly in remote sections of the Ozarks.
The repopulation of the Missouri River and its tributaries in north Missouri was the result of colonization by either remnants of the original population or migrants from farther upstream. Many of the beavers now living in southern Missouri presumably represent the production of six pairs purchased from a northern state and released in 1928 and 1929. It is thought that some beavers in south-western Missouri may have migrated in from the west. From 1939 until 1955, beavers were live-trapped throughout Missouri in areas with a large population and released in desirable localities. This program helped to re-establish this species in most counties of the state and to restore this valuable furbearer in sufficient numbers to permit an annual trapping season.
Habitat and home
In Missouri, beavers live in and along streams, rivers, marshes and small lakes. For their home in running water, they usually excavate a tunnel and den in a high bank, but in quiet water like lakes, marshes or backwater, they frequently construct a large, bulky lodge of tree limbs or other debris.
Habits
Beavers are well-known for their engineering skills, particularly in building dams. In Missouri, they may construct dams across small streams and the head-waters or diverted channels of large rivers; they also create a system of waterways for floating food and construction materials. Paths from feeding grounds to water become well worn and at the water's edge, may end in mud slides. Beavers generally confine their activities to within one-half mile (.8 km) of their home during the entire year.
When felling a tree, the beaver generally cuts the first notch at a convenient height and makes a second one about three inches below the first. The bark and wood between the notches are cut out chip by chip until the tree snaps and falls. The beaver cannot direct the angle at which the tree falls. Since most trees along streams tend to lean toward the water, they are cut on the leaning side-which is most easily reached by the beaver-and thus fall into the water.
Foods
In spring and fall, about half of their food consists of woody vegetation and half of non-woody vegetation.
In summer they eat little woody vegetation, but in winter they feed on it almost exclusively.
While beavers are primarily bark-eaters, they consume mostly the bark of tender twigs and the new growth between the outer bark and the wood of branches and trunks. They eat corn when it is available and various water plants.
Reproduction
The breeding season starts in January or February. The single annual litter is born in April, May or June and usually consists of three or four young. When the kits are born, they are completely furred and have their eyes open and incisor teeth visible. Although they are able to swim at birth, they seldom come out of the den and swim until about 1 month old. The kits are weaned at about 6 weeks of age but stay with their parents until approximately 2 years of age.
Importance
The search for beaver pelts was one inducement to the exploration and settlement of this country. In 1763, Pierre Laclede and August Chouteau founded a fur-trading post below the convergence of the Missouri and Mississippi rivers; by 1880 this settlement, St. Louis, was the raw fur center of the world. Currently, beaver pelts are used extensively in the manufacture of women's coats and as trim for other fur and cloth coats. The flesh is tasty.
The relationship of beavers to the land and its wildlife is intricate. For centuries, beaver dams have backed up silt-laden waters and subsequently formed many of the fertile valley floors in the wooded areas of northern North America. Beaver dams have stabilized stream flow, slowed down run-off and created ponds which profoundly influence fish, muskrats, minks and waterfowl.
In Missouri, beaver damage is usually slight. Beavers do take some corn, dam some drainage ditches and burrow into some protective levees, but only rarely do their dens cause crumbling of banks or do their dams back water over fields or roads.
Management
Destruction of a dam does not discourage beavers; they promptly rebuild it. Instead, an unwanted dam should be fitted with a pipe to lower the water level and reduce flooding. To protect trees from beaver cutting, the trunks should be enclosed in wire netting up to a height of three feet (.9 m).
