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American Beaver (Castor canadensis)

American Beaver Kit | Photo courtesy of the Wildlife Rehabilitation Center of MN | Wildlife Rehabilitation Center of Minnesota

Architect of Ecosystems

American Beavers are absolutely amazing creatures. They are aquatic rodents, and look a little like their cousin the Common Muskrat with their webbed feet and thick brown pelt. They are considerably larger, though, and have flat paddle-like tails.

American Beavers are one of the few creatures that actually create new ecosystems! As Paul Rezendes explains in his book "Tracking and the Art of Seeing";

"At first there would be a stream running through a forest, flanked by tall trees and thick undergrowth. Then the beaver would build a dam, and soon the trees were down, a pond formed, and more trees died because of the high water. In a few years, the banks were cleared and there was lush, herbaceous growth on the shore and lily pads and cattails in the warm, shallow water. Great blue herons and great horned owls nested in the dead snags, while smaller birds and mammals lived in the cavities. Wood ducks and other waterfowl stopped to feed and rest on the pond, then amphibians, reptiles, otters and muskrats moved in. Before long, a whole new ecosystem had been created." ( Rezendes, 90)

As Rezendes said, it often starts with a stream or small river running through a forested area. A Beaver comes along and wants to create a dam in the water, but observes that the stream is too narrow and too swift. It uses its teeth to fell trees in the surrounding forest and tear them into strips or planks which can be carried into the river and carefully positioned. Beavers often place large logs together like a fence, so that they will snag smaller debris carried by the current. When the structure of the dam is in place, they dig mud from the nearby banks and pile it on top, creating an extraordinarily sturdy structure. This is often no small feat. Dams have been recorded over six feet high, a mile long, and wide enough for a horse walk across (Rezendes, 91). These structures are maintained by extended beaver families and often take years to create.

Beaver lodges can also be marvels of engineering. They create lodges by first forming piles of trees, logs, branches and other debris. They then gather mud from the bottom of the pond, rolling it into a ball and op on to the top of the lodge, where they pat it into place with their tails. Entire families will work on lodges, and they will often take many years to build. Like muskrat lodges, the entrances are always underwater. Beavers that cannot create lodges (often because they are in the process of damming a waterway) will often dig burrows in banks. Lodges are much safer, as water deters many predators and a shell of frozen mud deters those who would attack the lodge during the winter.

Though nervous and somewhat awkward on land, Beavers are fantastic swimmers, and really built for the water. Valves close off their ears and nostrils when underwater, and a clear membrane protects the eyes. Only the front teeth remain exposed to carry wood and other debris. They can stay underwater for up to fifteen minutes before surfacing for air( Audubon Mammals, 570).

Interesting facts about the American Beaver:

• Beavers prefer the water, and don't like the land at all. They will often dig trenches, or canals, from ponds into wooded areas so that they can gather and transport wood more easily.
• There are active beaver lodges in many of Minnesota's state parks. Afton State Park has a particularly active one.
• The American Beaver Kit seen above was successfully treated by the Wildlife Rehabilitation Center of Minnesota and is now living at the Minnesota Zoo.
• Beaver mothers will carry their kits on their tail, or walk on their hind legs, carrying their babies in their forepaws.
• Beavers are, for the most part, monogamous.
• Their front "buckteeth" are the best tools the beaver has. The upper incisors act to support the lower incisors, allowing them to cut through even the toughest oak.
• Humans impact beaver populations through hunting and trapping, the destruction of habitat, and pollution.

Multimedia:

American Beaver | Afton State Park	American Beaver; trail indicator; lodge | Afton State Park

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	National Audubon Society's Field Guide to Mammals
	Tracking and the Art of Seeing

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