The beaver is proverbially a busy, industrious animal, noted as a natural lumberjack and “engineer.” Three hundred years ago, beaver were found throughout North America and over a large section of Northern Europe. Ironically, this busy, dam-building creature almost became extinct by the early 20th century because of its valuable fur. Since beavers require trees and water, the loss of woodland and the decline in water quality were also factors in the population loss. Fortunately, it is now becoming re-established in many areas.
The beaver is the largest rodent found in North America. The typical adult is about 30 inches long, about 12 inches high, and weighs about 30 pounds, though beavers have been known to grow to as much as 4 feet in length and more than 60 pounds in weight.
Its fur is a dark reddish-brown above, shading to a lighter brown or grayish color below. The beaver has a plump body, thick neck, and arched back. The flat, broad, scaly tail is about 10 inches long. The eyes are small, the ears are stubby, and the beaver is equipped with nostrils that can be closed completely to keep water out of the lungs during a long dive.
The hind feet are webbed for swimming, while the beaver’s forefeet have sharp claws and are used much as humans use their hands. Like all rodents, the beaver has front teeth that grow continuously. They wear away more rapidly in back, leaving a sharp front chisel edge that allow an animal to do its tree-cutting and woodworking.
Food and Diet
The inner bark of young tree or the higher, softer branches of such trees as the aspen, birch, and poplar form the bulk of the beaver’s diet. An animal will often fell a tree to get at those higher branches.
Beaver also eat the shoots, bark, and leaves of other trees, such as the alder, elm, oak, and willow.
When available, beaver will eat row crops, especially corn. Water plants also form part of the diet.
Beginning in late summer, beavers get busy cutting down trees and shrubs and transporting the bark and branches to underwater storage places so they will have plenty of food for the winter.
Beavers mate for life. The mating season begins in mid-winter, typically in January. After a gestation period of 107 to 110 days, the babies are born. A litter may range from one to six “kits,” as they are called, with three or four the most common number.
Kits are born with a full complement of fur and open eyes. They can swim at birth, though they don’t normally leave the lodge until they’re about a month old.
The mother suckles her kits in the lodge for about three months, while the male lives in a burrow on shore.
The education of the young beaver is also the mother’s responsibility, though the father acts as the primary food provider. The mother teaches her young what to eat and what trees to use for building.
The youngsters remain with the family for about two years. Then they leave and go off to establish their own colonies. Typically, they produce litters of their own when they’re three years of age.
On the average, a beaver lives three to four years in the wild, though a longer life is not unusual. Some animals have been known to live to 15 years and beyond.
Dams, Ponds, and Lodges
Beavers are very social animals. Families live together in a colony and they work together on their building projects.
The first step in establishing a colony is usually building a dam to form a beaver pond. The dam is made of brush and branches on a foundation of stones and mud. Wet vegetation and more mud form a plaster to hold it together.
At work in the water, a beaver swims with its hind feet, using its tail as a rudder while the forepaws are free to push debris aside or hold objects against the chest.
If danger appears, the beaver slaps the water with its tail to warn the other members of the colony and then dives for safety.
Beavers are very good swimmers, but they don’t move well on land, and it’s difficult for them to haul building materials any distance. As a result, they often dig canals so they can float the materials to the construction site.
Once the dam is built and the pond has formed, the lodge is built. This is the home for several beaver families.
The lodge is a large, dome-shaped structure made of wood and mud. Most of the lodge, including several entrances, is underwater, but it also includes a sizeable chamber above the water.
In some areas, rather than building the usual lodges, beavers dig burrows and shape dens in stream or river banks.
Burrows may go as far as 20 feet into the bank, and then a bark-lined chamber is built above the water level. The chamber is gradually reinforced with mud and sticks to form a conical lodge, known as a “half house.”
The Buttonwood Park Zoo’s beavers stay busy in their own section of the Aquatics Area.