Two species of beavers exist. The North American beaver (Castor canadensis), also called the Canadian beaver, is native to Canada, the United States and parts of northern Mexico. The Eurasian beaver (Castor fiber), native to Europe and parts of Asia, was nearly hunted to extinction in Europe, both for its fur and for castoreum, a scent gland secretion believed to have medicinal properties. This species is now being reintroduced throughout Eurasia.
North American Beaver
The North American beaver is the largest rodent on the continent. Its fur is a double coat consisting of long, coarse outer hairs that are normally dark brown and short, fine inner hairs. Its most notable characteristic is its long, flat, oval-shaped tail. Throughout its range, the beaver has long been trapped for fur for clothing and hats, a practice that nearly decimated populations in the early 19th century. Beaver numbers recovered with conservation efforts and are widespread once again with an estimated population of 10 to 15 million.
The Eurasian beaver is Europe’s largest native rodent. It looks very similar to the North American beaver, but it is larger and has a narrower muzzle and tail. The two species are not genetically compatible and cannot be interbred to create a hybrid subspecies. The Eurasian beaver was historically widespread in Eurasia, but trapping and hunting reduced its numbers from the millions to just 1,200 beavers in 1900. Today it is being reintroduced throughout much of its former range, and it now occurs from Great Britain to China and Mongolia. It remains extirpated from Italy, Portugal and the southern Balkans.
Both species of beaver are completely vegetarian. While they're commonly thought to feed only on wood, beavers enjoy aquatic plants, sedges, pondweed, water lilies, grasses and shrubs. They will also eat berries in the summer season. In winter months beavers gnaw the bark of birch, poplar, willow, quaking aspen, cottonwood, alder and maple trees. Their chewing often helps to stimulate new vegetative growth, aiding the revitalization and health of riparian zones. When the weather is cold, beavers will often store food underwater so that they can get to it from their lodges if pond water freezes over.
Beavers of both species build dams in rivers and streams, and they construct homes called lodges in the ponds created by their dams. Lodges are built using sticks, twigs, rocks and mud that beavers carry from the banks with their mouths and pack into place with their webbed paws and tails. Dammed ponds are still, secure areas around the lodges, which help beavers keep an eye out for predators. These ponds also create habitats for other species such as frogs, toads, water voles, otters, dragonflies, birds and fish.
Jennifer Bové is an award-winning contributor to "Your Big Backyard" magazine. She also writes for the National Wildlife Federation website and other online publications. Bové has published three books of nature-related stories, and she holds a B.S. in biology from the University of Missouri.