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Castor canadensis

Beaver Family (Castoridae)

Measurement: Size: 105 cm Weight: 16-30 kg

Description: No other animal has been as important to the growth and development of Canada as the beaver. As the symbol of the Hudson Bay Company, it was the most important fur-bearing animal on the continent. It is also impossible to mistake the beaver for any other animal. Look for a large, stalky rodent with bright yellow teeth, and an enormous tennis racket-like tail. Their tail forms an effective rudder when swimming, and is slapped on the surface of the water to warn of danger. They also have a special transparent membrane that can be drawn over the eye to protect it during diving. They can also close their ears and nostrils while submerged. The hind feet are webbed to provide strong propulsive forces when swimming. The front paws are not webbed and are quite dexterous for handling a variety of plants and for the building of dams.

Range: Beavers are found throughout Canada and much of the northern United States. They are also quite common throughout the Canadian and American Rockies. When beavers find a suitable location, they set to dam building to rise the level of the local watercourse. They begin by placing sticks vertically where the water flows the fastest, and then placing other materials in front of this first row. The process is continued until a strong dam is constructed. It will be packed with mud to help stabilize it. As the water level rises, they will eventually build their main lodge in the centre of the pond. This will have an underwater entrance which will protect them from predators.

Diet: Beavers are strict herbivores, relying on the leaves and bark of aspen trees as their main food source. They build their dams in areas of prevalent aspen stands, and as the stands are depleted, they will usually build a new dam downstream where fresh stalks are available. In this way they can leverage the benefit of the original dam.

Beavers are a welcome, but difficult to obtain food source for many large predators including otters, cougars, wolves and bears. The most effective predator is the otter which can simply enter the lodge through the main entrance to attack the beavers living inside. Other predators may try to dig their way through the roof of the lodge, but this is usually a very difficult task. Beavers are most vulnerable when they are on land, cutting trees and moving the materials to the waters edge. To reduce their exposure, they build canals that radiate away from the water to allow them quick access for fresh stands of aspen.

Reproduction: Beaver life is based upon monogamous mating pairs. They work together to build the dams and the lodge, and the female tends to select the dam site. They produce a single litter of between 1 and 9 (usually 3 or 4) each year. Gestation is approximately 100 days. The young may stay and become a productive part of the colony. The length of time they remain is limited largely by the availability of food. Usually they will disperse by their second or third year. With the birth of the kits, the male is temporarily evicted and must take up residence in a bank burrow while they are nursing.

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All Material Ward Cameron 2005



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