Beavers

The true beavers are robust, aquatic herbivores in the family Castoridae, order Rodentia. Many taxonomists believe that two, closely related species of true beavers exist—the American beaver (Castor canadensis) and the Eurasian beaver (C. fiber). Other taxonomists, however, classify these as closely related variants of the same species, under the name Castor fiber.

A few other rodents are also called beavers, such as the mountain beaver (Aplodontia rufa) of western North America, and the swamp beaver or nutria (Myocastor coypu) of South America. However, these two species of rodents are not in the family Castoridae, and are not true beavers.

The true beavers are large animals, weighing as much as about 88 lb (40 kg), and they are the largest rodents to occur in Eurasia and North America. Only the capybaras of South America (family Hydrochoeridae), which can weigh as much as 110 lb (50 kg), are larger rodents. However, a now-extinct species of giant beaver in the genus Castoroides, which occurred in North America as recently as about 10,000 years ago at the end of the most recent ice age, is estimated to have weighed several hundred pounds. This enormous rodent was similar in size to a black bear (Ursus americanus).

One of the most distinctive features of beavers is their scaly, naked, paddle-like tail. The flattened beaver tail is used as a rudder while the animal swims, using its webbed hind feet to propel itself through the water. The unusual tail is also used as a support while the beaver is standing and as a brace while the animal is dragging logs to the water. If danger is perceived, the tail is energetically splashed onto the water surface to warn other beavers of the threat. However, contrary to what some people believe, the tail is not used as a trowel to daub mud onto the dams that beavers often build.