Last Updated on Tuesday, 15 December 2009 10:39
Common Name: American Beaver
Genus species: Castor canadensis
- The American Beaver is the largest rodent in North America.
- Both sexes are similar in body size and colouration.
- Weight: 11-26 kg
- Body Length: 74-88 cm
- Tail Length: 26-33 cm
- The pelage consists of a thick, dark grey to brown undercoat that aids in retaining body heat, and a longer guard coat that is glossy brown to reddish in colour.
- The tail is used as a rudder, muscular and hairy at the base, with the remainder black, scaly, and paddle shaped.
- The hind feet are extensively webbed for swimming, with the claws on the first and second toes split in two for grooming purposes.
- The ears and nostrils are valvular, and the lips close behind the incisors to enable chewing while underwater.
- The eyes have a nictitating membrane to protect them while open underwater.
- The dental formula is: I (1/1), C (0/0), PM (1/1), M (3/3) = 20 teeth. Incisors are large, orange, and continually growing.
North American Distribution:
- They are found throughout the temperate region, from northern Mexico to the edge of the Arctic tundra.
- Within Alberta, Beavers are dominantly found in the Foothills, Parkland, and Boreal Forest Natural Regions.
- Beavers prefer forested riparian areas dominated by deciduous trees, such as aspen, cottonwood, and paper birch.
- Found along various types of water bodies, including ponds, lakes, slow moving rivers, and streams.
- Live in colonies of 4 to 8 individuals.
- Colonies often require 0.8 to 2.5 km of streambank or pond shoreline.
- Population densities vary with habitat quality (range 0.5-3 colonies/km2).
- Scent-marking is used to maintain territory boundaries, including a lodge, dams, and food caches.
- Beaver lodges are composed of interwoven twigs and branches, and then covered with a layer of mud, which freezes during the winter.
- Lodges include an underwater entrance, reducing predation, and a dry, raised platform within.
- Along large rivers, Beavers may excavate a den out of the riverbank as opposed to building a lodge.
- Dams are composed of logs, sticks, rocks and mud, inhibiting the flow of water.
- Dams average approximately 23 metres in length and may be 3 metres high.
- The purpose of Beaver dams is to raise water levels, therefore creating appropriate habitat for lodge construction and reducing the need for over land travel while foraging.
Movements and Migratory Habits:
Diet and Foraging Strategy:
- Beavers usually travel up to 45 metres from water to forage.
- Distance of travel for foraging is strongly correlated with size and species of tree; a larger aspen is preferred over a less palatable species of the same size, such as conifers.
- Activity levels are highest between dusk and dawn, and continue year-round.
- Territories are maintained so long as the dominate female survives; otherwise her mate will abandon the territory to find a new female.
- Juveniles will travel 4 to 5 km during dispersal.
- Timing and distance of dispersal is strongly correlated with the quality of the habitat.
- On occasion, a juvenile may inherit the territory from its parents.
- During the summer, non-woody vegetation is preferred, including leaves, twigs, buds, aquatic vegetation, and submerged roots.
- Throughout the winter, branches and sticks of deciduous trees, such as aspen, cottonwoods, and willows, stored throughout the summer in food caches are accessed by swimming under the ice.
- Food caches are an adaptation for northern living and are not utilized by southern Beaver populations.
- Beavers are monogamous and mate for life.
- Sexual maturity occurs between the ages of 1.5 and 3 years.
- Mating occurs during the annual breeding season, January to February.
- Gestation takes 90 to 110 days, with births occurring between April and June.
- A single litter including 2 to 4 kits, is born annually.
- Kits are born fully furred, with open eyes, weighing 230 to 630 grams.
- The young will nurse for two months before weaning.
- The parental male is responsible for bring solid food to the young; however, all members of the colony are known to partake in this task.
- Juvenile Beavers remain with the colony for approximately 2 years before dispersing.
- Provincial Status: Secure
- Federal Status: Not at risk
- The American Beaver is not currently of conservation concern.
- Trapping of beavers for their pelts has been occurring for hundreds of years.
- Beaver populations had been severely reduced by the 1900s.
- Regulated harvesting and transportation led to the re-establishment of Beaver populations throughout North America.
American Beaver photo © 2006 Simon Phipps. Retrieved from www.istockphoto.com/stock-photo-1815504-begging-beaver.php on 18/09/09. Used with permission.
Alberta Sustainable Resource Development (ASRD). 2008. Search Species and Status Category. <http://www.srd.gov.ab.ca/fishwildlife/speciesatrisk/statusofalbertawildspecies/search.aspx>. Accessed 20 Jan 2009.
Baker, B. W., and E. P. Hill. 2003. Wild Mammals of North America: Biology, Management, and Conservation. Second Edition. John Hopkins University, Baltimore, Maryland, USA.
Clutton-Brock, J., and D. E. Wilson, editor. 2005. Smithsonian Institution: Animal. Dorling Kindersley, New York, New York, USA.
Forsyth, A. 1985. Mammals of the American North. Camden House, Camden East, Ontario, Canada.
Muller-Schwarze, D., and L. Sun. 2003. The Beaver: Natural History of a Wetlands Engineer. Comstock, Ithica, New York, USA.
Nowak, R. M., and J. L. Paradiso. 1983. Walker’s Mammals of the World. Forth Edition. Volume 1. John Hopkins University, Baltimore, Maryland, USA.
Royal Alberta Museum. 2006. Creature Collection: Beaver (Castor canadensis). <http://www.royalalbertamuseum.ca/vcollects/detail.asp?Grp=Mammals&family=Castoridae&Genus=Casotr&Species=canadensis>. Accessed 20 Jan 2009.