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Beavers

At 4 feet long and 40 to 60 pounds, the American beaver (Castor canadensis) is North America’s largest rodent. It has a stocky body with glossy brown fur, short legs with webbed hind feet and a paddle-shaped tail. An aquatic mammal, it can spend up to 15 minutes underwater. Valves in its ears and nose close to keep out water, and clear membranes cover and protect its eyes. It can seal it lips behind its incisors so it can forage underwater, too.

Beavers are herbivores that eat the roots of aquatic plants, marsh grasses, corn, and tender twigs and bark from trees such as cottonwood, willow, aspen, birch and poplar. When a beaver cuts down a tree, it gnaws it into portable pieces, eats what it can and moves the branches to a nearby waterway. (Its two lower and two ever-growing upper incisors make smooth, distinctive cuts in wood.)

A beaver colony is made up of one family unit with a lifelong mated pair and offspring from two consecutive breeding seasons. Beavers have one litter in the spring with usually four young per litter. At two years of age, the offspring leave the colony and seek their own homes, thereby spreading the population along waterways and recolonizing vacant habitat.

Colonies may den in a riverbank or lakeshore but they usually construct lodges in the water. A lodge is a dome-shaped home of branches and mud that can rise 5 feet above the water. Lodges are warm and dry inside and accessible through underwater passages. Beavers create winter food supplies by anchoring large groups of branches and twigs into muddy pond bottoms around their lodges.

Beavers also construct dams out of branches stabilized with rocks and mud. Dams are important because a dammed stream becomes a pond that provides beavers with drinking water, travel routes and shelter.