Beaver (Rodent)

The beaver (Castor canadensis) is Canada's largest RODENT (15-35 kg). It has had a greater impact on the history and exploration of Canada than any other animal or plant species.

Description

The thick-set body of the beaver is covered with dark, reddish brown fur consisting of coarse guard hairs over dense, soft underfur. The large mass-to-surface ratio and the dense, insulating fur adapt it for a semiaquatic existence in water that can often be ice cold.

The black tail is horizontally flattened, paddle-shaped and scaly. Large, webbed hind feet are powerful paddles for swimming. The eyes are small and have nictitating membranes, which can be drawn across the eyeball when the beaver is underwater. In addition, the nostrils and ear openings have valves that can be closed at submersion. Finally, structural adaptations in the back of the mouth prevent water getting into the lungs and permit the beaver to gnaw under water and to carry branches while swimming submerged.

Other Species

At the end of the Pleistocene (10 000 years ago), Canada was also home to the giant beaver (Castoroides ohioensis) which was similar to its present-day counterpart except that it was bear-sized and had lower incisors almost 25 cm long. Giant beavers, like many other large herbivores such as mammoths and ground sloths, went extinct at that time, for reasons that are not clear. One other species exists, the European beaver (C. fiber).

Range and Habitat

Throughout its history, the beaver has been restricted to the northern hemisphere. Intentional introductions such as that in 1946 to Tierra del Fuego at the tip of South America has now allowed it to inhabit both hemispheres.

Beavers inhabit forested regions across Canada and north to the TREELINE, but are infrequent on the prairies. Typically, they occupy slow-flowing streams, where they construct dams of sticks, logs, debris and mud. The beaver is one of the only mammals, other than humans, that can manufacture its own environment. Beavers often build canals for floating logs to build dams. These dams maintain a water supply to protect their lodges, which are built of the same materials as the dams, and have entrances below water level and ramps leading up to living quarters above water.

Dams also provide greater access to the beaver's major food items: leaves, buds, twigs and bark of deciduous and (rarely) coniferous trees. Beavers also eat herbaceous pond vegetation.

Lodges are anchored in the mud of ponds and are made of intricately interlaced branches and stems of trees. Mud and grass are plastered around the outer walls. When the sub-zero temperatures of winter come to freeze a prison of ice around the perimeter of the lodge, it is all but impermeable to predators. While temperatures outside the lodge may range down to -40° C or more, inside the warmth of the animals always keeps the temperature around 8-12° C.

Habits

Beavers are superb swimmers, and can stay underwater for up to 15 minutes. When alarmed, they slap the water with their tails, warning others to take refuge underwater. Beavers are primarily nocturnal, carrying out most activities from dusk to dawn. They do not hibernate but regularly leave the lodge throughout the winter to obtain food from a submerged cache anchored nearby.

Beavers appear to be strongly territorial, being aggressive towards intruders. To advertise the limits of the territory, mud-scent mounds are placed strategically and castoreum, from the pear-shaped castor glands located in the anal region of both sexes, is regularly applied.

Reproduction

Beavers are monogamous, mating for life. Each beaver colony normally consists of 2 parental adults, the yearlings born the previous year and the newborn kits. Just prior to the birth of the young, 2-year-olds are forced to disperse from the parental colony. Beavers breed in January-February, have a gestation period of 3½ months and give birth to 2-4 young.

Biological Importance

Without beavers' dams, much of the water in the numerous small streams throughout Canada would flow unchecked through the landscape. By impounding water and felling trees, beavers not only provide themselves with wood for their lodges and twigs for their food, but they also open up dense woods, creating opportunities for a variety of plants and animals. Because of this, they have been called a keystone species in temperate and BOREAL FOREST aquatic ECOSYSTEMS.

Grasses, SEDGES and wildflowers spring up along pond margins. Aquatic and land insects thrive and provide food for song birds such as song SPARROWS, tree SWALLOWS and cedar WAXWINGS. Mergansers and other species of DUCKS, as well as KINGFISHERS, feed in the shallow waters. Beaver-killed trees provide nesting sites for cavity-nesting birds. Toads, FROGS and newts breed and thrive in the ponds, providing food for HERONS and RACCOONS.

The water and its surroundings attract MINK, MOOSE, MUSKRAT and OTTERS. Abandoned beaver ponds silt in and become grass meadows for DEER, VOLES and other herbivores. Thus, the activities of the beaver serve to increase the BIODIVERSITY of the forested regions of Canada.

Beaver was once considered the most valuable fur, particularly when felt hats made from the underfur were symbols of prestige. The pursuit of BEAVER PELTS from the Maritimes to the Mackenzie Valley led to the exploration of vast regions of what became Canada. When the FUR TRADE first started, it is estimated that there were 10 million beavers living in what is now Canada. By the time the fashion had changed in the mid-1800s, the beaver was almost extinct.

Today thriving populations of beaver occur once again across Canada. Because of the beaver's impact on the development and history of Canada, it is rightly one of Canada's national EMBLEMS, is on the coat of arms for the provinces of Alberta and Saskatchewan (see EMBLEMS, PROVINCIAL AND TERRITORIAL) and has been immortalized in 1000 PLACE NAMES across Canada.

Author R. BOONSTRA

Links to Other Sites
Beaver
A natural history of the beaver, the largest rodent in North America. Part of the extensive Hinterland Who's Who website.

Symbols of Canada
An illustrated guide to national and provincial symbols of Canada, our national anthem, national and provincial holidays, and more. Click on "Historical Flags of Canada" and then "Posters of Historical Flags of Canada" for additional images. From the Canadian Heritage website.

Canadian Biodiversity Website
A great information source for all budding biologists. Learn about biodiversity theory, natural history, and conservation issues. From McGill’s Redpath Museum.

Top 10 Things Canadians Should Know About Canada
Click on the 101things.ca link to discover the top 10 things people should know about Canada, a list developed from a national survey of what Canadians felt were the 101 people, places, symbols, events and innovations that most define our nation. From the Historica-Dominion Institute.

Giant Beaver
The natural history of the giant beaver (Castoroides ohioensis,) an animal that roamed across Canada’s landscape 10,000 years ago. From the Yukon Beringia Interpretive Centre.

Glossary: Hudson’s Bay Company
A bilingual glossary of key terms found the Hudson’s Bay Company records. From the website for the Hudson's Bay Company Archives. A PDF file.

Fur Trade Facts
A glossary of terms commonly used in reference to the history of Canada's fur trade. From the website for Alberta's Heritage Community Foundation.

World's Largest Beaver Dam at Home in Canada's Largest National Park
A photo and description of the world's largest Beaver Dam located in Canada's largest national park. From Parks Canada. Wood Buffalo National Park of Canada

Animals as National Symbols
See a listing of animals designated as national symbols for various nations. From the Minnesota Zoo.