Species Fact Profile: American Beaver (Castor canadensis)

                                                             American Beaver

                                                Castor canadensis (Kuhl, 1820)

Range: North America, including most of Canada, almost the entirety of the United States, and extreme northern Mexico  

Habitat:  Temperate Lakes, Ponds, Rivers, and Streams with ample vegetation

Diet:   Bark, Soft Tree Tissue (Willow, Poplar, Maple, Beech), Aquatic Plants

Social Grouping: Family groups of up to 8 individuals, a mated pair and their older offspring

Reproduction: Monogamous, but will repair in the event that one partner dies.  Both sexes sexually mature at about 3 years of age.  Mate between November and March (earlier in southern part of the range, later in the north).  Gestation period 105-107 days, usually born April-June. 1-4 kits are born fully-furred with eyes open.  Weaning may take anywhere from two weeks to three months.  Driven away from natal lodge at about 2 years

Lifespan: 10-12 Years

      Conservation Status: IUCN Least Concern 

• Largest rodent in North America (rivals the European beaver for largest rodent in the world after the capybaras).  Body length 90-117 centimeters long, weigh 13-32 kilograms (records of up to50 kilograms).  Specimens in the northern part of the range tend to be larger than ones in the south.  Hind legs are longer than front legs, making rear end appear high when walking.  Ears are short and rounded.  Tail is broad and flat, covered with large black scales
• Fur is a glossy red-brown or brown-black color.  Undercoat hairs are much finer than the protective outer guard hairs.  Glands are used for oiling and waterproofing the fur
• Teeth are disproportionately large, upper incisors often 0.5 centimeters wide and 2-2.5 centimeters long, grow throughout the animal’s lifetime.  Teeth are bright orange
• Adaptations of primarily aquatic lifestyle include webbed hind feet (front feet are unwebbed for greater dexterity and ability to dig), closable ears and nostrils, and transparent eye membranes.  Lips can close behind teeth to allow the beaver to gnaw while underwater.  Thick layer of subcutaneous fat for warmth 
• Families are territorial and will protect their range from other beavers, using both auditory (tail-slapping the surface of the water) and scent-marking (musk called castoreum from anal glands).  Limited vocalizations, including a whine, a hiss, and a growl
• Primarily nocturnal, usually becoming active around dusk.  Will wander considerable distances to find food; they may dig canals to help float food back to their lodge.  Food will be stored in snow or under the ice in the water during the winter, keeping it fresh and providing the beavers with food during the winter (do not store food in warmer climates)
• Microorganisms in the cecum allow the beaver to digest cellulose, a major component of their diet that many other mammals cannot digest
• Most famous for building dams to turn rivers and streams into slow-moving lakes and ponds, with the shape of the dam being dependent on the flow of the water (straight lines are preferred in slow water, curved dams in fast-flowing water).  Dams are built of branches and mud, packed into place.  Behavior seems to be triggered by the sound of running water.  In naturally—occurring lakes, beavers will forgo dam-building and dig burrows in the banks
• Beavers also construct lodges of wood, vegetation, and mud, with underwater access points for shelter.  Lodges are usually surrounded completely by water.  They may measure over 2.5 meters across and up to 1-meter-high, expanding over the years
• They are considered major landscape architect species which have an enormous impact on the habitat complexity, raising the water table and purifying water.  Trumpeter swans and other birds use the tops of lodges as protected nesting sites.  Waterfowl, fish, and turtles may rely on beavers to create habitat; many species are found at higher densities and with greater diversity in beaver ponds.  If beavers are killed or driven away, their dams eventually decay without maintenance and the pond become meadow.  Impacts of beaver reoccurrence in habitats in which they have been historically extirpated are being studied
• Mutualistic relationship with muskrats, which share beaver lodges and eat the food the beavers have collected while gathering fresh reeds for the lodge
• Natural predators include wolves, wolverines, bears, lynx, fisher, and possibly river otter, with young beavers and kits being more vulnerable than adults.  Alligators are a less-common predator; eagles may take kits.  Signal danger by slapping the water with their tail
• One of two species of the beaver, the other being the European beaver (Castor fiber), though another North American rodent, Aplodontia rufa, is sometimes called “mountain beaver.”  Efforts in Russian fur-farms to hybridize American and European beavers were unsuccessful (American beavers have 40 chromosomes versus 48 in Europeans), with only a single stillborn kit resulting from dozens to attempted pairings.
• Heavily hunted throughout history for their pelts (used in clothing, especially hats); access to fresh sources of beaver was a major drive for early exploration of the interior of North America, with wars fought over access to fresh beaver territories.  By 1900, the species was trapped out of large portions of its range
• Important food source for Native Americas, though meat has to be prepared in such a way to rid it of the musk flavor.  Like capybara, colonial Catholics considered beaver to be a “fish” so that it could be eaten during Lent
• Official mammal of Canada (featured on coins and stamps, including the first animal to be depicted on a stamp rather than a person), and state mammal of Oregon (often called the “Beaver State”) and New York in the United States
• Species has become invasive in Tierra del Fuego in southern Chile and Argentina, where it was released after failed fur-farming attempts.  Species has since spread, crossing saltwater channels to expand their range.  Beaver-modified habitats have also been shown to provide footholds for other invasive northern species, such as brook and rainbow trout.  Species was also introduced in Finland (at the time it was thought to the be same species as the European beaver and was brought in as a reintroduction attempt)
• In western culture most famous for its industriousness, with the expression “busy as a beaver”