ANIMAL ESTATE client 1.12: BEAVER
FROM ANIMAL ESTATES 1.0: NEW YORK, NY
SCIENTIFIC NAME: Castor Canadensis
RANGE: Beavers are found throughout all of North America except for the northern regions of Canada and the deserts of the southern United States and Mexico. (Frazier, 1996)
HABITAT: Beavers live in lodges, of which there are three types: those built on islands, those built on the banks of ponds, and those built on the shores of lakes. The island lodge consists of a central chamber, with its floor slightly above the water level, and with two entrances. One entrance opens up into the center of the hut floor, while the other is a more abrupt descent into the water. (Encarta, 2004) The lodge, itself, is an oven-shaped house of sticks, grass, and moss, woven together and plastered with mud. Over the years, repair and elaboration leads to an increase in hut size. The room inside may measure 2.4 m (8 ft) wide and up to 1 m (3 ft) high. The floor is blanketed with bark, grass, and wood chips. (Encarta, 2004) The pond lodge is built either a short way back from the edge of the bank, or partly hanging over it, with the front wall built up from the bottom of the pond. The lake lodge is built on the shelving shores of lakes. To ensure adequate water depth surrounding the lodge, beavers dam streams with logs, branches, mud, and stones. (Encarta, 2004; Toronto Zoo, 2000)
HOME CONSTRUCTION: Beavers often build narrow canals near trees and plants so that they can float them to the site of their new home. When a dam is built in a stream, it slows down the water flow preventing flooding and forming a still water pond upstream and the downstream side dries out. Still water organisms flourish as previous ones die off. After the dam is abandoned and breaks, water forms a pond downstream, leaving the moist, fertile soil above to develop into what is called a beaver meadow. Within the beaver dam is the lodge, a well insulated structure made of trees, twigs and dried mud, which keeps predators out. A vent at the top of the domelike enclosure keeps a constant exchange of air. Within the lodge, there are multiple floor levels, each for a specific action, such as sleeping. Beavers give birth in the lodge, and after a couple of years, the young leave home to build their own dam.
BUILDING MATERIALS: Sticks, moss, grass, and mud.
BUILDING MOTIVATION: Beavers build dams to slow down the flow of water in streams and rivers and then build stable lodges for shelter. The dams are engineered according to the speed of the water; in slow water the dam is built straight, but in fast water the dam is built with a curve in it. This provides stability so that the dam will not be washed away. ("Data: Species: Mammal: American Beaver- Castor canadiensis", 1998; Frazier, 1996; Hall and Kelson, 1959)
THREATS: Young beavers are very vulnerable, and are threatened by bears, wolves, wolverines, lynx, fishers and otters. An adult beaver's size is a deterrent to most predators, and though natural predators pose a very real danger to kits, man has proven to be, by far, the most dangerous predator to beavers. Killing beavers for their pelts, disrupting them through a change in habitat, and slowly poisoning them through pollution, which is known to infect wounds, all have lead to the threat which man poses on beavers. (Toronto Zoo, 2000)
INTERESTING FACTS: Beavers maintain wetlands that can slow the flow of floodwaters. They prevent erosion, and they raise the water table, which acts as a purifying system for the water. This happens because silt occurs upstream from dams, and toxins are then broken down. As ponds grow from water backed up by the damn, pond weeds and lilies take over. After beavers leave their homes, the dams decay, and meadows appears. (Frazier, 1996)
REFERENCES:
Anderson, R. 2002. "Castor canadensis" (On-line), Animal Diversity Web. Accessed October 30, 2007.
Frazier, Janice. 1996. Pittsburgh Zoo. Castor canadensis (On-line) (1 August 2002)
Hall, E. Raymond Ph.D, Kelson, Keith R. Ph.D. 1959. The Mammals of North America. vol. 2. The Ronald Press Company. NY.
Sevilleta Long-Term Ecological Research Project (LTER)/ RKM and KVP. University of New Mexico. 1995. Castor canadensis.
Sevilleta LTER. 1998 "Data : Species : Mammal : American Beaver - Castor canadiensis" (On-line) (1 August 2002)
1998. "Data: Species: Mammal: American Beaver- Castor canadiensis" (On-line). Sevilleta LTER Data. Accessed August 01, 2002.
Beavers: Wetlands and Wildlife. 2002. "The Beaver" (On-line). Accessed February 09, 2004.
Encarta, 2004. Beaver. Microsoft Encarta Online Encyclopedia. Accessed February 09, 2004.
Frazier, J. 1996. "Castor canadensis" (On-line). Pittsburgh Zoo. Accessed August 01, 2002.
Hall, E., K. Kelson. 1959. The Mammals of North America, vol. 2. New York: The Ronald Press Company.
Toronto Zoo. 2000. "Castor Canadensis" (On-line). Accessed February 15, 2004.
Whitaker, J., W. Hamilton. 1998. Mammals of the Eastern United States. New York: Cornell University Press, Sage House.