Beavers are among the largest rodents in the world. Two species of beavers exist today: the American beaver and the Eurasian beaver. Superficially, they are very similar. Both share the characteristic flat, scale-covered tails, webbed back feet and large, orange-colored incisor teeth. Though close in size, the Eurasian species is just slightly bigger than its American counterpart.
The American beaver (Castor canadensis), also called the North American or Canadian beaver, is found throughout North America, with the exception of Florida, the desert southwest and the Canadian high arctic. Small populations even extend into northern Mexico. The largest rodent in North America, adults range from 35 to 46 inches in length and weigh between 28 and 70 pounds. Their distinctive tail alone can be upwards of 15 inches long and 6 inches wide. At birth, young beavers, called kits, are nearly 15 inches long, including their tails, and weigh from 0.5 to 1.3 pounds.
Eurasian beavers (Castor fiber), once widespread in Europe and Asia, numbered just 1,200 individuals at the start of the 20th century, primarily caused by over-hunting. Today, the species has been restored to much of its former range across Europe and Russia. The largest rodent in Europe, adult Eurasian beavers range between 28 and 53 inches in length and weigh from 28 to 77 pounds. Newborn kit weights are nearly identical to those of their American cousins.
Shared Physical Characteristics
Both American and Eurasian beavers are well adapted to an aquatic existence. Webbed hind feet propel them through the water when swimming. The flat, hairless tails act as four-way rudders underwater and as counter balances when carrying materials for their dam building. Both species have valves to keep water out of their ears and noses when swimming, and nictitating membranes that cover their eyes underwater.
In addition to being slightly larger, Eurasian beavers have less rounded heads with narrower and longer muzzles; longer and narrower tails; and fur color that varies geographically, from grey to blackish brown. Despite their many shared characteristics, the two species are not genetically compatible. North American beavers have only 40 chromosomes, whereas Eurasian beavers have 48.
- Montana Outdoors: North American Beaver; Gary Beeler;
- Large Herbivore Network: Eurasian Beaver
- University of Michigan Museum of Zoology - Animal Diversity Web: Castor Fiber
- IUCN Red List of Threatened Species: Castor Canadensis (American Beaver)
- Idaho State University -- Idaho Museum of Natural History: American Beaver
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