How big is a beaver anyway?

Body length: 3 ft. (.9 m)
Height at the shoulders: 15 in. (38 cm)
Weight: 35 to 66 lbs. (16 to 30 kg)
Fur color: Overall brown.
Tail length: 1 ft. (30 cm)
Tail width: 6 in. (15 cm)
Tail color: Black.
Beaver is the common name for three species of rodent in two different taxonomical families, Aplodontidae and Castoridae. [1] Aplodontia rufa, or mountain beaver, is the only living species in the family Aplodontidae, and is native to the Pacific Coast of North America. The mountain beaver is smaller than the common beaver and resembles a muskrat. [2] The family Castoridae contains two species, Castor fiber (European or Eurasian beaver) and Castor canadensis (the common or true beaver). The Eurasian beaver formerly lived from the British Isles to eastern Siberia. Around the end of the 19th century, overhunting reduced Eurasian beaver populations to approximately 1,200 animals. However, thanks to protection, natural spread, and reintroduction during the 20th century, their population has risen to an estimated 593,000 animals in 2002. Currently, they are established throughout Europe except for Iberia, Italy, and the southern Balkans. They are also present in China, Mongolia, and Khabarovsk. [3] The common beaver or true beaver, C. canadensis, is native to North America. [4] [5] The common beaver is found from the Arctic to northern Mexico, except Southern California, most of Florida, Nevada, and parts of Alaska. There have been some reports of the isolated populations in Southern California, in Temecula Creek. [6]  [7] C. canadensis has been the official emblem of Canada since 1975. [8] Between the years 1853 and 1877, the Hudson Bay Company harvested over 3 million beaver for sell in England. Pelts were so valuable that they significantly contributed towards the westward settlement and development of North America and Canada. [9]  [10]

A beaver in the snow at Soda Butte Creek, Yellowstone National Park.
A beaver in the snow at Soda Butte Creek, Yellowstone National Park.
Image Source: NPS Photo by Jim Peaco

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Over trapping almost led to the North American beaver's extinction in the 1930s. [11] However, since then, laws have been enacted to protect them from overexploitation. These new laws, natural reproduction, and human reintroduction have now reestablished the North American beaver over most of the continent, to the point where they have become an agricultural pest in some regions -- a sure sign of success. [12]  [13] The beavers of the family Castoridae are the largest living rodent in the world, except for the South American capybara. [14]  [15] There are no special names for male and female beavers, however babies are called "kits." [16] In the wild, beavers will live about 10 or 12 years, although in captivity some have lived as long as 19 years. [17] Born for life in the water, a beaver can remain submerged for up to 15 minutes, and swim up to 5 mph (8 kph). [18]  [19] In water they primarily propel themselves with their webbed hind feet. Their flat spatula-like tail acts as a rudder, while they will hold their front feet tightly against their body. [20] When swimming at the surface, only the head is usually visible, unlike a muskrat where both the head and back are partly above the water. [21] On land a beaver walks or runs with a waddling gait, between 6 and 8 mph (9.7 and 12.9 kph). [22]  [23] A colony consists of a cluster of lodges, each occupied by a family. The family consists of a male and female and their last two litters, a total of approximately 18 animals. [24]  [25] One family of beavers may need half a mile of river habitat. [26] Although beavers are considered social animals and form monogamous bonds, they work independently and have little actual contact with each other. [27]

Image Source: LASZLO ILYES / License under Creative Commons 2.0

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Beavers live in streams, rivers, marshes, ponds, and shorelines of large lakes throughout North America, parts of Europe, and Asia. [28]  [29] The beaver is an environmental engineer -- second only to man in its ability to change the landscape for its own needs. [30] Beavers alter their environment on a large scale in order to provide themselves with shelter and protection. [31] However, this can often be a recipe for conflict with humans. Beavers flood roads, cut down trees, plug road culverts, and can even cause dangerous flash flooding when one of their dams break. [32] However, their dam building activity has a very beneficial side. Beavers build and economically maintain wetlands that soak up floodwaters from upstream, prevent erosion, raise the water table, and create an ecosystem that breaks down toxins and pesticides, purifying the water. [33] Beavers prefer to dam streams in shallow valleys, by cutting down small trees and clearing brush. Much of the flooded area will become wetlands. Insects lay eggs in wetland environments. Fish, ducks, frogs, turtles and birds feed on the insects and larvae, and other animals in turn feed on them. [34] The biodiversity of a wetland can rival a tropical rain forest. As many as half of the endangered species in North America rely upon wetlands. [35]  [36] These marshy wetland areas also selectively allow certain trees to grow, that in turn, support different species of wildlife that require riparian (relating to the banks of a natural course of water) environments. [37] Other mammals, such as otters, will feed on the fish, and birds like ospreys, will nest in the dead trees that are killed by the flooding of the beaver pond. [38] In time, sediment will fill in the pond behind the dam and become a meadow. Shrubs will begin to grow and provide shade for tree seedlings. When the tree seedlings get tall enough, they will shade out the shrubs and eventually turn into a mature forest. Beavers help to begin this natural cycle, which is called forest succession, by building their dams. [39]

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Taken from "Beaver Facts and Natural History" by Samuel W. Fall
Copyright © 2007 Beaver Pictures & Facts

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Image Source for beaver lodge at top of page: M. LeFever, U.S. Fish and Wildlife Service.
Image Source for two beaver at bottom of page: Tom Smylie, U.S. Fish and Wildlife Service.