The beaver is a bulky animal with a large, scaly, paddle-shaped tail. Adults typically weigh 40 to 50 pounds, but some may weigh over 90 pounds. The front feet are small with long, sharp, curved toe-nails while the hind feet are large and webbed. The eyes of a beaver are small and dark. The body fur is usually dark brown above and lighter below; the tail is blackish.
The beaver is the largest member of the rodent family in Illinois. Like other rodents, it has two upper and two lower teeth located at the front of its jaws that are called incisors. Used chiefly for gnawing, a beaver's incisors are long, massive and sharp.
These specialized teeth allow a beaver to cut through a willow tree that's 5 inches in diameter in about a minute! Four upper and four lower teeth located on the sides of the jaws are short, square and used for grinding food.
Distribution & Abundance
Beavers are common and live in every county in Illinois.
Beavers live in streams, rivers, marshes and lakes. Every area in the state that has suitable food sources (primarily tree species like maple and willow) located near permanent water is potential beaver habitat.
Beavers are well known for their engineering skills, especially building dams across streams and small rivers. The dams hold back water, increasing its depth and surface area. This gives the beavers better protection from predators and closer access to food. More importantly, the deeper water keeps the underwater entrances of their dens from freezing over easily during winter. Dams are usually built in a narrow place in the stream, often where logjams or rocks already constrict the flow of water. Sticks, weeds, rocks and other debris are lodged together then backfilled with mud dredged up from the bottom. More sticks and mud are added as the water level rises. Dams 4 to 7 feet in height are common.
A flurry of beaver activity occurs in September and October as beavers prepare for winter. Dams are built up and kept in good repair. Tree saplings are cut and anchored underwater outside the lodge or den. This feed pile can reach a size of 3 to 6 feet deep and 30 to 40 feet across. When ice forms, the beavers swim out of the underwater den entrance, cut branches from their feed pile and return to their den to eat the bark.
Most of the family's time is spent above a main dam, but they sometimes add one or more smaller dams downstream to back up water against the base of the main dam. This relieves much of the water pressure that might cause the main dam to rupture. Secondary dams also give them better access to food located downstream. Beavers sometimes dig a system of channels for towing food and construction materials where the water is too shallow to swim comfortably.
Beavers fell trees by cutting the first notch at a convenient height and then making a second one about three inches below the first. They chew out the bark and wood chip by chip until the tree snaps and falls. The beaver is unable to drop a tree in a specific spot or at a specific angle. However, most trees that grow along streams tend to lean toward the water, so they usually fall into the water when cut.
Beavers confine their activities to within one-half mile of their lodge or den. They're most active at night, dusk and dawn. Daytime activity is rare except during the breeding season, when the ice melts in springtime, and in areas with little human disturbance.
Beavers construct bank dens and lodges for shelter and raising their young. They prefer bank dens if the stream bank is suitable for construction. Starting below the water level, they dig into a stream bank, often where it's steep and held together by tree roots. Angling upward, they dig until this tunnel clears the water level by a foot or two. Beavers then hollow a chamber large enough to sleep and move around. They add one or more den entrances, fanning out in different directions. They scatter wood in the chamber to keep it dry. They repair minor cave-ins when part of the bank collapses by piling sticks and mud on top of the hole.
Beavers build lodges in marshes where the banks are too flat to dig bank dens. In these locations, beavers pile sticks and mud until they have a dome-shaped structure that rises well above water level. They then tunnel into it starting below water level.
Groups of beavers that live together are called colonies. The typical colony starts out as a pair of beavers that are at least two years of age. About 3 to 4 young are born in the spring. Another litter is born the following spring, bringing the colony size to as many as 8 to 12. Young from the first litter (now 1 1/2 to 2 years old) leave on their own by the next fall or are driven off by their parents in the spring to make room for another litter. From this time on, the cycle repeats itself each year so that adults and young from no more than two successive litters are in a colony. Those that leave, look for places to start their own colonies.
Beavers eat the bark of tender twigs and the new growth between the outer bark and the wood of branches and tree trunks. Preferred tree species include willow, river birch and maple. Roots of aquatic plants, marsh grasses, clover and even certain berries are spring and summer fare. They seldom eat pine trees, but sometimes cut them for building purposes.
Breeding starts in January or February. A single annual litter of 3 to 4 young is born in April, May or June. Some females have as many as six or seven kits. When the kits are born, they are completely furred, with their eyes open and front (incisor) teeth visible. Although they are able to swim at birth, they seldom come out of the den until they are about one month of age. The kits are weaned at about six weeks old but remain with their parents until 1 to 2 years of age.
Beavers were common in Illinois during the early 1800s. Without laws to protect them, their numbers declined so much from hunting and trapping that they were no longer considered an important part of the fur trade by 1850. Only a few colonies remained at the turn of the century, and protective regulations enacted in 1933 proved to be too little too late. Whether beavers were extinct for a period of time in Illinois is unknown, but with the possible exception of the Mississippi River bottoms of JoDaviess County, it seems likely.
The reintroduction of beavers in Illinois began in 1929 when the U.S. Fish and Wildlife Service released an adult male and a female on the Savanna Ordinance Depot in JoDaviess and Carroll counties. They released 16 more at this location in 1936. In 1935, the USDA Forest Service stocked 19 beavers in Pope County. In 1938, the Illinois Department of Conservation released the last two reintroduced beavers in Union County. These efforts were probably aided by movements of beavers into Illinois from neighboring states like Iowa and Indiana, where similar restoration programs were underway.
From 1946 through 1951, beavers were live-trapped in areas with high populations and released in areas with low numbers. This program was so successful that the number of beavers available for relocation from sites where they were causing damage eventually outpaced the need for restocking efforts. During December 1951, a 15-day trapping season was opened to help curb complaints associated with flooding, tree damage and crop loss. Longer seasons with fewer restrictions were put in place as the statewide population grew.
Although beavers provide many ecological benefits, these benefits must be weighed against threats to human interests like agriculture, transportation and even endangered species conservation. Laws that restrict trapping to certain times of the year protect beavers while keeping damage complaints in check and allowing a sustainable harvest.