The Life of a Beaver. Building Dams and Canals

Beavers usually live in family groups. As many as 12 beavers may make up a family, but generally there are 6 or fewer. The group includes the adult male and female, the young born the year before, and the newborn.

Beavers live as long as 12 years. Their enemies include bears, lynxes, otters, wolverines, wolves, and people. A beaver avoids these enemies by living in the water and by coming out mostly at night to eat or work.

The young. A female beaver carries her young inside her body for about three months before they are born. She has two to four babies at a time. Most young beavers, called kits or pups, are born in April or May. A newborn kit is about 15 inches (38 centimeters) long, including its tail, and weighs ½ to 1 ½ pounds (0.2 to 0.68 kilogram). The tail is about 3^ inches (8.9 centimeters) long. A kit has soft, fluffy fur at birth, and its eyes are open.

The young live with their parents for about two years, and then are driven from the family group. These young adults are forced out to make room for the newborn. Beavers rarely fight with each other except in spring, when the 2-year-olds are driven away.

Food. Beavers eat the inner bark, twigs, leaves, and roots of trees and shrubs. Poplar trees, especially aspens and cottonwoods, and willow trees are among their favorites. One acre (0.4 hectare) of poplars can support a family of six beavers for one to two years. Beavers also eat water plants, and especially like the roots and tender sprouts of water lilies.

Beavers store food for winter use. They anchor branches and logs in a cache under the water near their lodges. In winter, they swim under the ice and eat the bark.

Cutting down trees. A beaver uses its strong front teeth to cut down trees and to peel off the bark and the branches. To cut a tree, the beaver stands on its hind legs and uses its tail as a prop. It places its front paws on the tree trunk, and turns its head sideways. Then the beaver bites the trunk to make a cut in it. The animal makes another cut farther down on the trunk. The distance between the two cuts depends upon the size of the tree. The cuts are farther apart on large trees than on small ones. The beaver takes several bites at the cuts to make them deeper. Then the animal pulls off the piece of wood between the cuts with its teeth. It keeps cutting and tearing out pieces of wood until the tree falls. Beavers usually cut the wood away around a tree trunk, but they may cut through the trunk from only one side.

A beaver cannot control the direction in which the tree falls. It cuts until the trunk starts to break, and then runs to safety. The animal usually dives into the water nearby. It waits there until it is sure that no enemies have been attracted by the noise of the falling tree. Then the beaver goes back to work on the tree.

First the animal gnaws the branches off the tree. Then it carries, drags, pulls, pushes, or rolls the log into the water. The beaver stores some branches deep in the water for use as food during the winter. The other branches may be used to enlarge or repair the dam and the lodge. Beavers often work alone, but sometimes several work together.

Where beavers live. The yellow areas in the map, below, show the parts of the world in which beavers are found. Most beavers live in North America

Building dams and canals. The beaver's habits of building and of storing food seem to be instinctive (un- learned). A beaver cuts down trees even if it has no place to build a dam or a lodge, and even if it has more than enough food.

A whole beaver family, and sometimes beavers from other families, may join in building a dam. Beaver dams are made of logs, branches, and rocks plastered together with mud. Beavers use mud and stones for the base of a dam. Then they add brush and log poles. They strengthen the dam by placing the poles so that the tips lean in the same direction as the water flows. The beavers plaster the tops and sides of the poles with more mud, stones, and wet plants. They do most of this work with their front teeth and front paws. They bring mud from the river bottom by holding it against their chests with their front paws.

The beavers build their dam so that the top is above the water. Some dams are more than 1,000 feet (300 meters) long. Beavers may keep their dams in good condition for many years. Most beavers that live in lakes do not build dams, but some build dams across the outlets of small lakes.

A beaver marks its territory with castors, small piles of mud mixed with the beaver's scent. The castor glands of beavers are used in making perfume.

Sometimes beavers dig canals so they can move logs to their dams or lodges easily and quickly. The canals are 12 to 18 inches (30 to 46 centimeters) deep, 18 to 24 inches (46 to 61 centimeters) wide, and may be more than 700 feet (21 meters) long. A beaver canal may extend from a wooded area to a lake or riverbank. Or it may cut across a piece of land that sticks out into the water.

A beaver colony bustles with activity. Beavers cut down trees to build a dam and repair their lodge. They store food in a cache for winter, and take twigs into the lodge for the young

Building lodges. A beaver lodge looks somewhat like a tepee. A family of beavers builds its lodge with the same materials and in much the same way as it builds a dam. The lodge may stand on the riverbank or in the water like an island. The tops of most lodges are 3 to 6 feet (91 to 180 centimeters) above the water. Each lodge has several underwater entrances and tunnels, all of which lead to an inside chamber. The floor of the chamber is 4 to 6 inches (1 to 15 centimeters) above the water. Here, young beavers can stay warm and dry in winter, and the adults can dry off after bringing in food. Holes between the branches in the ceiling let in fresh air.

The size of the lodge depends on the size of the family and the length of time the beavers have lived there. The animals enlarge and repair the lodge as long as they live in it. Most beavers abandon their lodge only if they have eaten all the food in the area, or if too many enemies move nearby.

Beavers that live in large lakes or in swift rivers may dig dens in the banks. These beaver dens, like the lodges, have underwater entrances and tunnels.