Castor canadensis
American beaver

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)

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)

Beavers are primarily aquatic animals, and the largest rodents in North America. They have a waterproof, rich, glossy, reddish brown or blackish brown coat. The underhairs are much finer than the outer, protective, guard-hairs. The ears are short, round, and dark brown in coloration. A beaver's hind legs are longer than its front legs, thus making the rear end to be higher than the front end while walking. ("Data: Species: Mammal: American Beaver- Castor canadiensis", 1998; Frazier, 1996; Hall and Kelson, 1959; Whitaker and Hamilton, 1998)

Beaver skulls and teeth are disproportionately large. This is crucial for cutting through hard woods like maple and oak. Most noteably, the upper incisors, bright orange in color, are at least 5 mm wide and 20-25 mm long. These teeth grow throughout the animal's lifetime and are a necessity to survival, just as the animal's closable nostrils, closable ears, and transparent eye membranes are for aquatic existence. (Hall and Kelson, 1959; Whitaker and Hamilton, 1998)

Also notable are the anal and castor glands, found in both male and female beavers. Both sets of glands lie at the base of the tail, which is possibly the most defining characteristic of the beaver. It is broad, flat, and covered in large blackish scales. The anal and castor glands have been recorded as large as 3.4 by 2.2 inches for the castors, and 3.0 by 1 inch for the anal glands. Secretions from these glands are used in scent-marking, and give the beaver its odd odor. (Frazier, 1996; Hall and Kelson, 1959; Whitaker and Hamilton, 1998)

Beavers also have anal and castor glands, which they use to mark their territory. These glands are located beneath the tail. A beaver's tail is broad, flat, and covered with large black scales. (Frazier, 1996; Hall and Kelson, 1959; Whitaker and Hamilton, 1998)

Under favorable conditions, beavers will produce their first litters at two or three years of age. The average lifespan of a beaver in the wild is 10 to 20 years. While its size saves it from most predators, a beaver's lifespan can be cut short by predators, most commonly humans, wolves, and coyotes. Parasites and disease also play a factor in mortality. (Frazier, 1996; Whitaker and Hamilton, 1998)

Beavers usually live in family groups of up to 8 related individuals called colonies. The younger siblings stay with their parents for up to 2 years, helping with infant care, food collection, and dam building. Beaver families are territorial and defend against other families. One method is territory marking. This is done by making mud piles around the edges of a territory, and then by depositing anal and castoral secretions on these piles. Beavers will also warn others of danger by slapping their tails against the water, creating a powerful noise. This, however, is not always effective, as olders beavers will often ignore the warning slaps of younger members of the colony. ("Data: Species: Mammal: American Beaver- Castor canadiensis", 1998; Frazier, 1996; Hall and Kelson, 1959; Whitaker and Hamilton, 1998)

Beavers are primarily nocturnal. They are only occasionally seen during the day, usually around dusk. Beavers travel good distances from their homes to find food. If they find a good source, they build canals to the food source as a way to float the food back to their lodges. Logs and twigs are often stored underwater for winter feeding. ("Data: Species: Mammal: American Beaver- Castor canadiensis", 1998; Frazier, 1996; Hall and Kelson, 1959)

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)

Beavers have a pair of anal scent glands, called castors, which secrete a musk-like substance called castoreum. This is used mainly for marking territories. The broad, flat, scaly tail is about 25 cm (about 10 in) long and serves as a warning signal when slapped against the water. Beavers also call out to others, making a low, groaning sound. (Beavers: Wetlands and Wildlife, 2002; Encarta, 2004)

Beavers eat bark and cambium (the softer growing tissue under the bark of trees). Their favorites include willow, maple, poplar, beech, birch, alder, and aspen trees. They also eat water vegetation, as well as buds, and roots. Cellulose, which usually can not be digested by mammals, is a major component of their diet. Beavers have microorganisms in their cecum (a sac between the large and small intestine) that digest this material. In zoos, beavers are fed yams, lettuce, carrots and "rodent chow." (Frazier, 1996)

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)

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)

Although beavers are beneficial to the environment, they can destroy it also. Dams slow the flow of water in fast streams, changing the flora and fauna and sometimes creating silting. They may flood low-lying areas, sometimes causing extensive loss of timber. ("Data: Species: Mammal: American Beaver- Castor canadiensis", 1998)

Beaver fur has been a significant trade item for the last century, creating large amounts of money for merchants.

Beavers are incredibly beneficial to the environment. They are instrumental in creating habitats for many aquatic organisms, maintaining the water table at an appropriate level and controlling flooding and erosion, all by building dams. See the Sevilleta Long-Term Eocological Research Project (LTER)/ RKM and KVP-- University of New Mexico account on the web at http://sevilleta.unm.edu/animal/mammal/beaver.html for a more detailed explanation of the benefits of beavers in the environment. ("Data: Species: Mammal: American Beaver- Castor canadiensis", 1998)

The conservation status differs with respect to source, but there have been significant threats to the survival of the beaver. Beavers have been hunted and trapped extensively in the past and by about 1900, the animals were almost gone in many of their original habitats. Pollution and habitat loss have also affected the survival of the beaver. In the last century, however, beavers have been successfully reintroduced to many of their former habitats. ("Data: Species: Mammal: American Beaver- Castor canadiensis", 1998; Frazier, 1996)

One of the earliest accounts of beaver natural history was written by Samuel Hearne in the late 1700s. His journal entry on beavers is online at: http://web.idirect.com/~hland/sh/an020.htm.