Alberta, Canada
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American Beaver
Castor canadensis
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General Description

By Gustave J. Yaki

The American Beaver, one of two living species (the other is European), is our largest rodent. Their most characteristic feature is their broad, flat, paddle-shaped, scaly tail, often slapped on the water surface as a danger signal. Beavers may grow to 120 cm (roughly 4 feet) in length and weigh up to 45 kg (almost 100 pounds). A much larger Giant Beaver once lived here. It died out about the time that the North America Mammoths, Mastodons, Horses, Camels, Giant Bison, Giant Sloths, American Lion, Sabre-toothed Tigers, Short-faced Bears and several other large life-forms disappeared, about 10,000 years ago.

Beavers and humans have a lot in common. Both build houses (lodges) and dams. However, when humans build dams, we often destroy or degrade the habitat (homes) of most other species, but when beavers do so, most other species benefit. Without beavers, we would have continuous wooded areas; there would be few marshes and swamps, and as a result, few or no freshwater fishes, ducks, muskrats, cattails, arrowheads and hundreds of other species of plants and animals that require water and sunny areas in which to live.

Their dams are constructed on streams, usually in the narrowest and shallowest sections. Beavers may choose these sites in response to the sound of running water for they can also be induced to build at inappropriate places by continuously playing tape-recorded sound of trickling water. Their dam, contructed of fallen timber, branches, other vegetation, rocks and mud and is always well engineered. They seem to inherently know that to successfully resist the pressure of rising water, that the dam must be a shallow U-shape, with the bottom of the U upstream. Perhaps modern human dam engineers first learned this from beavers. Beavers usually build a cone-shaped lodge in the deep pool that they create. This is also made of wood. After a sizeable mound is assembled, sometimes topping two m above the water surface and up to ten m long, an entry tunnel is cut well below the water surface. This leads to a resting platform or den that is chewed out above the high water mark. The stick surface is then plastered with mud, except for a small vent area, allowing for the escape of stale, humid air and the entry of fresh air. The mud-covered surface freezes solid during the winter preventing any predators that travel on the ice to gain access at that time. Occasionally, where there is permanent deep water, rather than build a lodge, some beavers dig a tunnel in a steep bank for their living quarters.

Beavers spend most of the winter months in their lodge, exiting only to retrieve pieces of the stored branches on which to feed. Here they mate, usually in January or February, occasionally later. Four months later, a litter of four kits are born. They grow quickly, and begin to gnaw when still less than a month old. They are weaned at two to three months of age. A second litter is sometimes also produced. The young, which help in dam renewal and construction, and refurbishing the lodge, stay with their parents well into their second summer, after the birth of the new kits, leaving only then to make winter room for the new young In summer, beavers eat a variety of green plants. At the onset of winter, they are provident, planning ahead to be able to eat the bark of poplars, their favourite food trees. They somehow recognize them in the dark of the night (without a flashlight), then cut them down with their chisel-sharp teeth, reducing them into smaller pieces which are dragged or floated to their impounded area and anchored underwater, dining upon them when ice on the surface no longer allows them to come ashore. In cutting these poplars, this allows more sunlight to reach the ground next spring, enabling seedling trees such as White Spruce, which were nursed but shaded by the poplars, to quickly grow, providing food and nesting sites for hundreds of other species.

Beavers front teeth (incisors), grow at a tremendous rate; if kept in captivity and fed only soft vegetable matter, with nothing to chew to wear down those teeth, they curl inwards, puncturing the roof of their mouth, eventually killing them. When not disturbed, beavers prefer to work by day. They are often seen at dusk along the Elbow and Bow Rivers in Calgary. A loud warning splash made by their wide, flat tail is often the first indication that they are moving about.

The American Beavers range covers all of North America from northern Mexico to the limit of trees in the arctic. It is the unofficial mammal symbol of Canada, appearing on the five-cent coin. Canada was first explored by those intent on obtaining their pelts, which led to their near extinction by 1860. The pursuit of their furs eventually led to the opening up of this country for newcomers from Europe and eventually from the rest of the world. Without the beaver, perhaps non-native humans might never have colonized this land.

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Where to find American Beavers in Alberta   

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