North American Beaver (Castor canadensis)

May 12, 2011

by Lorraine Julien

While gathering firewood on our property this past February, we came across the handiwork of a very experienced logger – the beaver. His handiwork was evidenced by the number of fallen young birch trees on our island. While we usually harvest damaged or dying trees for our woodstove, this fellow just chooses the very best healthy trees! Placing the fallen trees exactly where he wants them is also no problem for this logger/engineer. Usually you have to trim the branches from fallen trees but this was already done for us so we just cut the trees into manageable sizes and carted them across the ice to the shore with toboggans.

A beaver can cut down a 5” thick tree in about three minutes and can cut down more than 200 trees a year. Their preference in trees is not very limited – for example, we’ve had to put protective wire around a couple of young maples near the water’s edge. Even young oak trees may fall victim to this four-legged logger: my brother had a tall, young oak growing alongside his deck. He decided he would transplant the tree to another area on the property. Before this could be done, the tree was cut down, at ground level and entirely removed with not a scrap of bark, chips or any hint that the tree had ever been there!

When logs or other building material are too heavy and need to be moved, Mr. Beaver simply builds a canal to float the material. In fact, beavers’ ability to change the landscape is second only to humans. That is one of the reasons why we find this flat-tailed species so fascinating.

Preferred foods are water lily tubers, and the bark of birch, poplar and willow trees. In summer, they may eat berries and apples, if available. Even though beaver ponds provide fish habitat, beavers are strictly herbivores and do not eat fish.

Of course, beavers are famous for their dam-building ability, much to the chagrin of municipal workers who are constantly trying to keep roadway culverts clear.

The main reason that beavers build dams though is to provide a moat around their lodge to deter predators such as coyotes, wolves and bears and to provide easy access to a food cache during the winter. Dams are built first with vertical poles; then the space between the poles is crisscrossed with horizontal branches. Gaps are filled in with a combination of stones, mud and weeds until the dam can hold sufficient water to surround the lodge. In late fall, the lodge is covered with a layer of mud which freezes into a cement-like coating. Predators can cross the ice but cannot penetrate the fortress-like lodge.

While other wildlife endure wintertime cold and hunger, beavers stay cozy and warm in their lodges. Once spring arrives, the underwater entrance to the lodge makes it almost impossible for predators to enter.

A beaver colony may consist of six or more including parents, yearlings and kits, yet they peacefully co-exist. Once kits leave the safety of the lodge and venture into the pond, they are susceptible to many predators including hawks, owls and otters. Beavers rarely overpopulate because they breed only once a year. Two-year-olds leave home in search of their own territories, always near waterways.

Once the population of a pond reaches a certain level, beavers have fewer kits. When adults are removed from an area, the remaining survivors have larger litters to compensate (a phenomenon similar to coyotes and some other mammals).

A beaver pond provides much more than protection for beavers – many wild creatures take advantage of the watery habitat including frogs, toads, fish, water fowl, muskrats, mink and otters to name a few. Raccoons, deer and, occasionally a black bear, may forage near the water’s edge at twilight. Many birds such as bluebirds, phoebes, catbirds, kingfishers, etc. prefer their nests near water.

Some beaver facts:

Its paired orange incisors hone each other to a chisel edge

If the beaver can’t gnaw on wood, it dies; otherwise the teeth would continue to grow and curve inward eventually piercing its skull

Two glands at the base of its tail contain castoreum, an oil that keeps the fur slick and waterproof

Its tail, a scaly paddle about 16 inches long, is used as a rudder, and an alarm-sounder when slapped on the water

Typical adults weigh 40 to 60 lbs. (18 to 27 kg.); however, I did read about one beaver trapped in Wisconsin that weighed 110 lbs. (50 kg.)

Each webbed hind foot is as wide as a ping-pong paddle and fully webbed

It can swim at five miles per hour, easily out-swimming a diver in racing flippers; and can stay underwater for up to 15 minutes

With split nails on the two inner toes, it oils its fur, combs out lice, and has been seen picking splinters out of its teeth!

It helps to purify water - fecal coliform and streptococci bacteria excreted into streams by grazing cattle have been shown to be reduced by beaver ponds where the bacteria are trapped in bottom sediments

The world’s longest beaver dam can be seen from space! It is 850 meters (2,790 feet) long and is more than twice the length of the Hoover Dam (which spans 1244 ft.). This huge dam is located on the southern edge of Wood Buffalo National Park in northern Alberta. Probably several beaver families joined forces to create the dam that contains thousands of trees and would have taken months to complete. (This information was taken from the May 4, 2010 issue of the Telegraph, a U.K. newspaper. The cartographer who discovered the dam was looking for signs of climate change; more dams are appearing in the north as the climate warms.)

Please feel free to report any observations to Lorraine Julien at This email address is being protected from spambots. You need JavaScript enabled to view it.  or Steve Blight at This email address is being protected from spambots. You need JavaScript enabled to view it.