Beaver

Castor canadensis missouriensis Bailey

A beaver working on its dam.
Color photo by Kristof Zyskowski.
   Copywrite 2001. All rights reserved.

Description:   The beaver is the largest living rodent in Kansas, and can be distinguished from other Kansas mammals by: 1) heavy, "humpbacked" body, 2) head which has a square profile and blunt muzzle, 3) small eyes and ears, 4) large, bright orange incisor teeth, 5) large black tail horizontally flattened, paddle-like, and covered with large scales except for the well-furred base, 6) short from legs with five toes and well-developed toenails, 7) large hind feet with five fully webbed toes, 8) three outer toes on the hind foot having normal nails, while the second toe is modified as a double claw, and 9) dense underfur of upperparts soft, silky and lead-gray, over which are long, coarse, dark brown guard hairs. Sexes are alike, and young are lighter than adults. It is difficult to determine the sex of a beaver by its external appearances.

Size:   Adults may attain the following dimensions; total length 940-1212 mm; tail 290-410 mm; hind foot 160-192 mm; ear 33-35 mm. Most adults weigh from 14-27 kgs; one exceptionally large beaver from Kansas weight 44 kilograms.

Range and Habitat:   The semi-aquatic beaver is found throughout Kansas wherever there are bodies of water and food trees.

Reproduction:   Beavers breed in January and February and after a gestation period of 110-120 days, one to six (usually three or four) young (kittens or kits) are born in May or June. The kits are born furred with eyes open and incisor teeth erupted, weigh about one pound, and nurse from two pairs of nipples. In six to eight weeks they begin to wean, but may nurse sporadically for another month or more, and remain with their parents until they become sexually mature, usually two years later. The adults, yearlings, and kits constitute a family unit.

Habits:   There is no other Kansas mammal that makes its presence known or controls its community more than beavers. They are active throughout the year from evening to morning and, when not disturbed, sometimes during the day. In the water, their head creates a wake across the surface, while on land they move with an awkward walk, or even gallop with tail swinging from side to side. The most conspicuous signs of beavers are well developed trails leading up stream banks to trees that they have felled and dragged back to the water. Some of these trails lead several hundred feet from the shore, but most are only a short distance from riparian vegetation. In shallow stream channels, canals are dug to food trees and are used to float the limbs back to the river or lake. Small trees, mainly cottonwood or willow and ranging up to 200 mm in diameter, are preferred as winter food but trees 1.2 to 1.5 meters in diameter have been felled (even hard oak trees are large as a meter in diameter). Small trees (three to five cm in diameter) can be cut be beavers in less than a minute; large trees may take several days. The tree falls in whatever direction it is leaning; small branches are then cut by the beaver into convenient size and transported to water. Branches and trunks too large to portage are left behind, but all the inner bark that can be reached is consumed. If the tree falls intro water the problem is reduced. Larger limbs are used for building beaver lodges or dams, or stored for winter use. Small limbs stripped of bark along the edge of a river are a good sign that beavers are in the area.

  If water in streams or ponds is not deep enough for beaver activity, one or several dams are made of limbs, placed with the large end facing upstream, and plastered with mud and wet vegetation. Beaver dams are conspicuous, but are only constructed in relatively small streams of fairly constant flow and low gradient.

  A beaver house or lodge is a round structure rising above the water surface, constructed of branches, and sealed with mud. It is also a conspicuous sign of beaver activity. An underwater entrance leads to a cavity in the middle of the lodge. Along rivers too large to dam, beavers construct dens by burrowing into the bank. Like the lake or pond lodge, the living platform in a bank burrow is above water level. Another important, but inconspicuous, structure is a shallow concavity along a riverbank or shoreline where beavers sit and preen themselves, or rest just out of the water.

  Beavers are monogamous and a mated pair may live together 10-15 years. As many as eight to 12 beavers, as a family unit, may live in a lodge, although the average is about five.

Food:   Winter food consists of inner bark from trees and shrubs. Branches anchored to a pond bottom or along a river edge near the lodge or bank den entrance are used when the water is frozen. The food is consumed by swimming under the ice and bringing the branches to the inside of the lodge. In spring and summer, aquatic plants and green shoots and plants growing near water are consumed, as well as willow leaves and twigs.

Remarks:   Coyotes and bobcats prey upon beavers, especially the young, and wolves were formerly a threat. Some beavers live 20 or more years in captivity. Other than the danger signal produced by striking water with its flat tail as it dives, beavers are seldom heard, but young sometimes can be heard in a lodge. Beavers can remain submerged beneath water for 15 to 20 minutes. Scent from the musk glands of a beaver may be deposited on mounds of mud at the water's edge as territorial markers of the colony, and are recognized as such by other beavers.


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