Living with Beavers in DuPage County

Scientific Name:Castor canadensis

Natural History

Although once extinct in DuPage County, beavers are again making their homes in many of our rivers, streams and lakes. The number of beavers in the county is difficult to estimate, but 17 to 21 colonies were located on District land during the winter of 1989.

One of the largest aquatic rodents at 40-60 pounds, the beaver once played an important role in the settlement of North America. Trappers were lured throughout North America by the valuable beaver pelt. In the early 1800s, Chicago was the busy fur-trading post, Fort Dearborn. DuPage County owes its name and the name of its main river to a French fur trader named DuPhaze.

So popular were the beavers' flesh, fur and leathery tail that the animals' numbers steadily dwindled from the 1850s until the turn of the century. It became extinct in Illinois in the early 1900s. From 1929 to 1936, attempts were made to reintroduce the beaver in Illinois. By 1954, beavers had dispersed to almost half the counties in the state.

Dam building is an important element in the beaver's survival. Dams are constructed of branches of cottonwoods, willows and other trees cut by the beaver and stabilized with rocks and mud. A damned stream becomes a pond providing water for drinking, a travel route and a home site.

A beaver colony is made up of one family unit. Each family consists of a lifelong mated pair and offspring from two succeeding breeding seasons. Usually, there are four beaver in the spring-born litters. At two years of age, the beaver offspring leave the colony and seek their own home site, thereby spreading the beaver population along waterways and re-colonizing vacant habitat.

Colony members usually construct a dome-shaped home of branches and mud in the water. The lodge is warm and dry inside, sometimes rising five feet above the water, and is accessible through underwater passages. Beavers may also dig a tunnel and den in a riverbank or lake shore. The only evidence of a bank den may be submerged and floating sticks near the underwater entrance.

Most active after sundown, beavers are strict vegetarians and will eat tender twigs, roots of aquatic plants, marsh grasses and corn. Favorite tree barks include cottonwood, willow, aspen, birch and poplar. Beavers store their winter food supply under water, anchoring large groups of branches and twigs into muddy pond bottoms around their lodges.

Identification

Telltale signs of a beaver's presence are a dam, conical-shaped tree stumps and diagonally cut branches. The cuts made by the beaver's sharp, ever-growing front teeth can be seen as smooth cuts in the wood. Once a tree is cut down, beavers will eventually gnaw it into portable pieces, eat the bark from the trunk and branches, and move branches to the nearby waterway.

Often people confuse a beaver in the wild with its smaller "cousin," the muskrat. The most distinctive feature of the beaver is the large, scaly and paddle-like tail. The tail is used as a rudder while swimming, as well as a warning signal to other beaver if it is slapped against the water.

The beaver's trademark is its large front teeth. Two ever-growing upper and lower incisors are essential tools for its lumberjack activities. A full-grown beaver is about four feet long, including the one-foot tail. Its body is stocky with short legs, sharp front claws and webbed feet. Its glossy coat is tan to dark brown, with coarse over-hair, and a fine, dense under-fur.

Control

Light, inexpensive wire fencing (minimum of three feet high) is the simplest long-term solution for keeping beaver out of waterside property, or to protect clusters of trees. The lower three feet of individual trees can be wrapped with heavy gauge hardware cloth. Remember to loosen the wire as the tree grows.

Live or kill trapping are poor alternatives. These activities must be permitted by the Illinois Department of Natural Resources. Destroying the beaver dam will not discourage these tenacious animals. They will build a new one, seemingly overnight. The beaver will eventually move on only if you are more persistent in tearing down the dam than they are in rebuilding it.

Beavers in DuPage County forest preserves generally are left alone in accordance with the District's statutory responsibility to manage its land in as natural a state as possible. Hunting and trapping are prohibited in the forest preserves.

Flooding on preserves is not controlled unless it causes public danger. However, if a dam in a preserve is causing flooding upstream on private property, the District will regulate the water levels on District property by placing a drain pipe in the dam to control the water level, or may remove the dam to discourage the beaver.

Beavers do not play as important a role in DuPage County as they once did. While some people consider beaver a nuisance, they have some positive points. For example, beaver dams at Pratt's Wayne Woods Forest Preserve in Wayne have improved the fishing and wildlife habitat. Beaver ponds also help replenish the underground water supply.