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Beaver (Castor canadensis)

Beavers are the largest rodents in North America, ranging in weight from 30 to 75 pounds, with an average length of 45 inches including the tail. They are found near wooded ponds and streams. Beavers are primarily aquatic and are excellent swimmers. They use their hind feet, which are webbed, and large, flat tail to propel themselves around the pond. They are adapted to life in the water, and can stay under for up to fifteen minutes.

Beavers are crepuscular, meaning they are active at the twilight times of dawn and dusk. The saying ‘busy as a beaver’ holds true, as these mammals are constantly building and repairing lodges and dams, and foraging for the vegetation which they eat. It is easy to know a beaver is in the area even if you do not see the animal. There are many different signs that indicate a beaver is present:


Beaver houses may vary in size. They are basically huge piles of sticks and mud hollowed out from the inside. Some animals begin construction of their lodge by using a tree that has tipped over, exposing the roots. Others dig into the soft mud found on the banks of a pond, similar to muskrats. Once a suitable location is found, the beaver piles sticks and pushes up mud and debris on the lodge using his two front paws, not their tails as shown in cartoons. The entrances, usually two, are underwater. Inside the lodge there is a dry platform and a sleeping area.
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Dams: Beavers build dams for two good reasons, food and protection. They begin by cutting larger trees and placing them with the branches facing upstream. The branches catch other debris in addition to the sticks and mud placed there by the beaver. Some dams can be quite large, others very small. Sometimes, beavers will build a series of dams down a stream.

Beavers are strict vegetarians, and the aquatic vegetation that grows in ponds supplies summer food. The favorite plants of the beaver are duckweed, pickerel weed, cattails, and spatterdock. Since beavers are slow moving on land, they are much safer swimming in the beaver pond they create by building a dam.

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Cut trees: Beavers have many uses for the trees that they cut down. They cut the trees by standing on their hind legs, using their tails for balance. A ring is chewed around the tree using the upper incisors. Like most rodents, beavers teeth grow continuously throughout their lives. The large incisors have a special coating of enamel, which wears away more slowly than the rest of the tooth. This gives the beaver a sharp biting edge. A beaver’s chewing force is 176 pounds per square inch, compared to man’s 88 pounds.

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     During the winter, beavers subsists on the inner layer of bark, the cambium. The rest of the wood is not wasted. It is used for dam and lodge maintenance and expansion.
     The favorite trees of beaver are willows, aspens, cottonwoods and alders.They also eat birches, oaks and maples and highbush blueberries. Some trees they do not like, such as hemlocks and pines, are usually girdled and left standing. These dead trees serve as homes to many forest creatures

There is no limit as to the size of the tree that beavers may cut. They will use small saplings that are taken in one bite, or larger trees which then have to be cut into sections to move. They seem to prefer trees that are three to four inches in diameter. If you find a tree that was felled by a beaver, look for the wood chips on the ground. Newly cut trees are blonde in color, those that are approximately a year old appear a silvery gray, and those that were cut over three years ago are gray and commonly have turkey tails, a type of mushroom, growing on them.

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Canals: When beavers run out of resources (trees) near the pond, they will dig canals to nearby areas with better habitat. This way they do not have to leave the water.

Winter Caches:

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Winter Caches: Look for branches sticking up outside of the lodge when ice forms. This is the winter food supply that was collected during fall. They cut down surplus food, and anchor it into the bottom of the pond with mud. Beavers do not have to go far from the lodge and waste energy breaking through the ice to get food.

Scent Mounds (or Castor piles): How a beaver marks territory. The piles are started by placing mud and leaves in a clump in a prominent area near the pond, and then a yellowish substance is deposited on the top if it. This substance is called castoreum and is secreted from a scent gland near the tail. If you find a scent mound, smell it. This is a sure sign that there are beavers in the area.


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Beavers walk the same path over and over again, and drag their tails behind them, wiping out any tracks that may be left in the mud. The well worn trails are seen coming in and out of the water. By looking carefully at these, you may come across a track. The beaver has five toes on both front and hind feet, and large nails that leave deep impressions. The back feet are webbed.

Scat: Beavers normally defecate in the water, so look for scat when the ponds dry up in the summer or where the water is shallow and clear. Scat is very hard to find. Winter scat resembles little balls of sawdust.

Mating occurs in January and February and 2-6 kits are born in April or May. A beaver family works together building and gathering food. The family is made up of the parents, the young from the previous year, and the current kits. At the end of their second year, they young are forced to leave the lodge. They often move downstream, creating a chain of beaver ponds following a watercourse.

In 1764, beavers were trapped out of Massachusetts. Today, there are upwards of 54,000 beaver, (compared to the 26,000 in 1996) Beavers have reached nuisance levels in some areas. With very few natural predators the number of beaver is only going to increase in the bay state.