Beaver (Castor canadensis)
General Characteristics Length: 900 - 1,200 mm (36-60 in.) Weight: 15 to 35 kg (33 to 77 lbs)
Physical descriptions: Their thick dark brown, waterproof coat has long glossy guard hairs overlying a very dense insulating undercoat. They have a paddle-shaped tail acting as a rudder, webbed feet, and valvular ears and nostrils that can be sealed when the beaver is submerged. The flattened tail and webbed hind feet are black. Their heavy, broad incisor teeth are dark orange-chestnut on the outside surface.
Habitat Beavers commonly inhabit riparian areas of mixed coniferous-deciduous forests and deciduous forests containing an abundance of beaver foods and lodge building material. They build their own lodges along streams where conditions are suitable for building a dam to form a pond. These lodges consist of a mound of branches and logs, plastered with mud.
Food Habits Beavers are herbivores that enjoy feeding on bark and cambium (the softer growing tissue under the bark of trees) of deciduous trees. Their favorites include willow (Salix spp.), aspen (Populus tremuloides), maple (Acer spp.), cottonwood (Populus spp.), birch (Betula spp.), alder (Alnus spp.), and dogwood (Cornus spp.). Also eaten is aquatic vegetation, such as duck-potato (Sagittaria spp.), duckweed (Lemna spp.), pondweed (Potamogeton spp.), and water weed (Elodea spp.) are the preferred foods when available, as well as buds, and roots.
In areas where their pond freezes over, beavers collect food in late fall, storing it underwater where it can be accessed through the winter. Tree limbs up to 5 inches in diameter, including the leaves, buds and bark are stored in dams or in front of bank dens where they will be peeled for food and eaten later in the winter.
Signs of Beaver One sign of beaver presence in the area include cuttings from trees that produce wood chips as well as tree bark shavings, as illustrated in photo to the left.
Beavers prefer to fell small trees 2 to 6 inches in diameter. They use the whole tree, cut limbs and mud to build their dome-shaped lodge and dams. This activity usually leaves behind drag marks where parts of trees have been transported overland; these often obscure the foot tracks.
Another sign of a beaver's presence is the production of scent from their castor glands that creates a reddish stain on mounds of grass and mud that they build at the water's edge.
They also clear trails through vegetation that grows out of shallow water sometimes, these runways can be seen at the bottom of clear water ponds. Sometimes visible on the stream bank is a slick surface made as beavers slide into the water.
Beavers have large webbed hind feet and produce tracks up to six inches in length. A tail mark is sometimes produced in soft mud.
Behaviour Beavers are active year round. They build dams to slow down the flow of water in streams and rivers and then build lodges for shelter. They maintain their pond-habitat by reacting quickly to the sound of running water and damming it up with trees, branches and mud.
Beaver Damage Before beginning any beaver control action, assess the beaver problem fairly and objectively. Are beavers really causing damage or creating hardship requiring control action? You should also determine the type of damage or problem the animal(s) are causing and then match the most appropriate and most cost effective control(s) to the situation.
Beavers can damage all species of trees. Trees up to 3 feet in diameter can be felled and larger trees can be girdled. Girdling removes the bark completely around a portion of a tree trunk, essentially killing it. Even partially girdled trees can suffer. After felling the trees the remaining stumps are easily identified as beaver damage by their pencil-tip shape and teeth marks in the exposed wood, as seen to the left. Wood shaving around the base of the stump may be found, along with trampled paths leading to water.
Beavers clip seedlings, saplings and branches from felled trees as food sources, especially in autumn. The clean, diagonal cut is diagnostic of beaver damage. Some branches may be completely stripped of bark. Broadleaf trees are preferred as food, especially smaller poplars and aspens, but almost any tree species of any size, including conifers, will be used especially when located close to their lodge.
Beaver problems not only include girdling or cutting down valuable ornamental trees and shrubs but also undermining of yards, walks and roadways with their burrowing.
How to Prevent Beaver Damage Once you have decided to control beaver damage, you have two control options:
- Prevention - protect trees with stucco wire to prevent or reduce the damage,
- Destroy the problem beaver and remove the dam
Since live trapping and relocating beavers are often cost prohibitive, their use is limited and often not practical. Also, research has shown that these methods of control are of questionable value because translocated beaver either return to the problem area or seldom survive relocation.
Prevention would include wrapping the affected area trees with a wire mesh such as stucco wire as opposed to chicken wire. The mesh should be at least half-inch diameter and installed around the tree trunk at least 4 inches away from the trunk. In other words, you are building a fence around a tree to protect if from the beaver. The fences should protect exposed roots and be at least 4 feet high. The fence should be braced with posts to prevent beaver from knocking it down or be buried into the ground about 0.5 to 1 inches. Illustrations above demonstrate proper placement of wire mesh. However, prior to taking any action regarding prevention of beaver damage consultation should be made with your local conservation or naturalist services offices.
Ecosystem Role Beavers maintain wetlands by slowing the flow of floodwaters and helping to reduce rapid rain runoff. They prevent and reduce soil erosion, contribute to the stabilization and rise of water tables, which acts as a purifying system for the water. This happens because silt occurs upstream from dams, and toxins are then broken down in the beaver pools. Dams also help reduce soil erosion and improve soil quality, since runoff deposits in quiet pools near beaver dams. As ponds grow from water backed up by the dam, pond weeds and lilies take over. After beavers leave their homes, the dams decay, and meadows appear. As a result, beaver habitat is often rich in plant and animal life, making beaver ponds excellent sites for observing nature.
Did You Know?
- Beavers have the ability to close their noses and ears while swimming underwater, and they have a clear eyelid to protect their eyes from the water and debris.
- Both mother and father beaver play a part in providing food for the young and protecting them from predators.
- A large liver enables the beaver to store much oxygen in its blood allowing it to remain under water for up to 20 minutes.
- The large front incisors of beaver grow continually throughout its life. These incisors are bright orange on the front and are continuously sharpened as they cut and girdle trees.
- The life span of beavers in the wild is approximately 10 to 12 years.
- The beaver's diving reflex helps to conserve heat and oxygen by slowing the heart, thereby reducing blood circulation to the extremities.
- Beaver are nocturnal and often begin their activities shortly after sundown.
- Beaver dams are engineered according to the speed of the water; in slow water the dam is built straight, but in fast water the dam is built with a curve in it.
- In order to warn each other of danger, beavers slap their tails against the water, creating a powerful noise.
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