Beaver

SCIENTIFIC NAME

Castor canadensis

DESCRIPTION

The beaver Castor canadensis is the largest rodent in North America and the largest rodent in the world except for the capybara of South America. An adult weighs from 16 to 32 kg and, including its 30-cm tail, a large beaver may measure 1.3 m long. Its ancestors were even larger. In the Pleistocene ice age—the era of the mastodons and the mammoths—the giant beavers that inhabited the expanses of Eurasia and North America measured just under 3 m in length, including the tail, and probably weighed 360 kg.

RANGE

Beavers are found throughout Canada, north to the mouths of the Mackenzie and Coppermine rivers on the Arctic Ocean. In the rest of North America, the beaver’s range extends throughout southwestern Alaska and most of the states south of the 49th parallel. The beaver has been exterminated in some states, and in practically all of its former range in northern Mexico.

HABITAT

Most common in forested areas, beavers also expand into unforested habitats, where there are water-courses bordered by deciduous trees or shrubs. Each day, beavers alternate periods of activity and rest. They are most active from dusk to dawn. Midday generally finds them in the lodge, be it summer or winter. The beaver’s life is inextricably connected to logging—or sustenance and for habitation. This animal cuts down an average of 216 trees a year. It can fell trees up to about 40 cm in diameter. Usually a single beaver cuts a tree, but sometimes two work on a large one.

DIET

All winter the beavers bring sticks from their underwater cache into the feeding chamber of the lodge to gnaw the succulent bark. They prefer trembling aspen, poplar, willow, and birch; half a hectare of aspen will support one beaver for a year. They also swim out under the ice and retrieve the thick roots and stems of aquatic plants, such as pond lilies and cattails. During mild winters and warm days in March and early April, adult beavers emerge from their dull aquatic world to feed on fresh woody stems along the shore. On such forays they often fall prey to hungry wolves. Beavers shift from a woody diet to a herbaceous diet as new growth appears in the spring. During summer, beavers will eat grasses, herbs, leaves of woody plants, fruits, and aquatic plants.

BEHAVIOUR

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PRIMARY ECOSYSTEM ROLES

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