General Information

There are two different species of beavers: Castor fiber and Castor canadensis. Castor fiber inhabits wooded areas of Europe and Asia, while Castor canadensis inhabits wooded areas of North America. (Sun and Mueller-Schwarze, 2003)

Differences between Castor fiber and Castor canadensis

Table table adapted from Table 1.1 in Sun and Mueller-Schwarze, 2003

Beavers are one of the largest rodents in the world, with some adults weighing up to fifty pounds ("Beaver: Canadian Domain," 2004; Linzey and Brecht, 2004). Like other rodents their front teeth grow very quickly and allow them to gnaw at dense vegetation such as tree trunks and branches ("Beaver: Canadian Domain," 2004). Beavers use the vegetation to build lodges and dams, and they eat the bark off of certain hardwood trees for food ("Beaver: Canadian Domain," 2004). Gnawing on this vegetation is actually very important for beavers' survival. If a beaver's teeth are allowed to grow uncontrolled the mouth will be forced permanently open, and the beaver will starve ("Beaver: Canadian Domain," 2004).

Trees Whittled by Beavers

Image courtesy of Eva Kattner from http://www.biologie.uni-ulm.de/bio3/biber/bib_project.html	Courtesy of Michael Leps of Natur-Lexikon.com

Beavers are well adapted for their aquatic environment. They have webbed hind feet and flat, broad tails that aid in swimming. They also have ocular membranes to protect their eye when swimming. Beavers are able to submerge for up to fifteen minutes. They also have thick dark fur that provides good insulation in extreme cold. This is especially important for beavers living in more northern latitudes. Beavers use castoreum, a liquid substance that they produce from a sex gland, to waterproof their fur. ("Beaver: Canadian Domain," 2004)

Webbed Feet and Tail

Image courtesy of http://sevilleta.unm.edu/data/species/mammal/socorro/profile/american-beaver.html

Beavers are nocturnal, which explains their relativity poor sight in comparison to their senses of hearing and smell (Sun and Mueller-Schwarze, 2003). They rely heavily on these two heightened senses for communication within their habitat (Sun and Mueller-Schwarze, 2003). The scent excreted by beavers is individual-specific, so scent mounds are used frequently in identification of individual beavers (Sun and Mueller-Schwarze, 1998). Beavers use their heightened sense of smell in recognition of kin, intruders, and predators (Rosell and Czech, 2000; Sun and Mueller-Schwarze, 1998).

Like most other monogamous species, beavers have reduced sexual dimorphism, sometimes making it difficult to distinguish between males and females during observation. However, there are subtle ways of distinguishing the two sexes. Depending on the species, females will have lighter or darker anal gland secretion (AGS). In Eurasian beavers females have darker AGS, and in the North American beaver they have lighter AGS. In addition, while offspring are suckling, the females will have larger and more obvious teats. This method, however, can only be used at certain times during the summer when the young are suckling. Another way of sexing beavers is to actually handle one and distinguish whether or not it has a baculum or a "penis bone." The bone feels like a bean and is located around the abdomen. (Sun and Mueller-Schwarze, 2003)

Beavers mate when they are about three years old, and gestation lasts from 100 to 110 days ("Beaver: Canadian Domain," 2004). Kits are able to swim only a few hours after birth ("Beaver: Canadian Domain," 2004; Linzey and Brecht, 2004). Dispersal age is usually around two years ("Beaver: Canadian Domain," 2004). At this time the young will go out and try to find territories of their own (Sun and Mueller-Schwarze, 2003). Occasionally two-year-olds will remain with the family if good territories are scarce (Sun and Mueller-Schwarze, 2003). A beaver's life span in the wild is usually ten to twelve years (Linzey and Brecht, 2004).