C. fiber – Eurasian beaver C. canadensis – North American beaver †C. californicus
Distribution of C. fiber.
Distribution of C. canadensis.
Fossils of C. californicus
The BEAVER (genus CASTOR) is a large, primarily nocturnal ,
semiaquatic rodent . Castor includes two extant species, the North
American beaver (Castor canadensis) (native to North America) and
Eurasian beaver (Castor fiber) (
* 1 General * 2 Etymology
* 4 Habitat
* 4.1 Dams * 4.2 Lodges * 4.3 Water quality and beavers * 4.4 Urban beavers in United States * 4.5 As an introduced non-native species
* 5 Social behavior
* 5.1 Family life * 5.2 Territories and spacing
* 6 Commercial uses
* 6.1 Trapping
* 7 In culture
* 7.1 As a national emblem * 7.2 In dietary law * 7.3 In computer science
* 8 References * 9 Further reading * 10 External links
Beavers, along with pocket gophers and kangaroo rats , are
castorimorph rodents, a suborder of rodents mostly restricted to North
America. Although just two closely related species exist today,
beavers have a long fossil history in the Northern Hemisphere
beginning in the
Beavers are known for their natural trait of building dams on rivers and streams, and building their homes (known as "lodges") in the resulting pond. Beavers also build canals to float building materials that are difficult to haul over land. They use powerful front teeth to cut trees and other plants that they use both for building and for food. In the absence of existing ponds, beavers must construct dams before building their lodges. First they place vertical poles, then fill between the poles with a crisscross of horizontally placed branches. They fill in the gaps between the branches with a combination of weeds and mud until the dam impounds sufficient water to surround the lodge. A beaver skeleton A beaver skeleton
They are known for their alarm signal: when startled or frightened, a swimming beaver will rapidly dive while forcefully slapping the water with its broad tail, audible over great distances above and below water. This serves as a warning to beavers in the area. Once a beaver has sounded the alarm, nearby beavers will dive and may not reemerge for some time. Beavers are slow on land, but are good swimmers, and can stay under water for as long as 15 minutes.
Beavers are herbivores, and prefer the wood of quaking aspen , cottonwood , willow , alder , birch , maple and cherry trees. They also eat sedges , pondweed , and water lilies .
Beavers do not hibernate, but store sticks and logs in a pile in their ponds, eating the underbark. Some of the pile is generally above water and accumulates snow in the winter. This insulation of snow often keeps the water from freezing in and around the food pile, providing a location where beavers can breathe when outside their lodge.
Beavers have webbed hind-feet, and a broad, scaly tail. They have poor eyesight, but keen senses of hearing, smell, and touch. A beaver's teeth grow continuously so that they will not be worn down by chewing on wood. Their four incisors are composed of hard orange enamel on the front and a softer dentin on the back. The chisel-like ends of incisors are maintained by their self-sharpening wear pattern. The enamel in a beaver's incisors contains iron and is more resistant to acid than enamel in the teeth of other mammals.
Beavers continue to grow throughout their lives. Adult specimens weighing over 25 kg (55 lb) are not uncommon. Females are as large as or larger than males of the same age, which is uncommon among mammals . Beavers live up to 24 years of age in the wild.
The English word "beaver" comes from the
The North American and Eurasian beavers are the only extant members of the family Castoridae , contained in a single genus , CASTOR. Genetic research has shown the modern European and North American beaver populations to be distinct species and that hybridization is unlikely. Although superficially similar to each other, there are several important differences between the two species. Eurasian beavers tend to be slightly larger, with larger, less rounded heads, longer, narrower muzzles, thinner, shorter and lighter underfur, narrower, less oval-shaped tails and shorter shin bones, making them less capable of bipedal locomotion than the North American species. Eurasian beavers have longer nasal bones than their North American cousins, with the widest point being at the end of the snout for the former, and in the middle for the latter. The nasal opening for the Eurasian species is triangular, unlike that of the North American race, which is square. The foramen magnum is rounded in the Eurasian beaver and triangular in the North American. The anal glands of the Eurasian beaver are larger and thin-walled with a large internal volume compared to that of the North American species. The guard hairs of the Eurasian beaver have a longer hollow medulla at their tips. Fur colour is also different. Overall, 66% of Eurasian beavers have pale brown or beige fur, 20% have reddish brown, nearly 8% are brown and only 4% have blackish coats. In North American beavers, 50% have pale brown fur, 25% are reddish brown, 20% are brown and 6% are blackish.
The two species are not genetically compatible. North American
beavers have 40 chromosomes , while Eurasian beavers have 48. More
than 27 attempts were made in Russia to hybridize the two species,
with one breeding between a male
North American beaver
Eurasian beaver (Castor fiber) was nearly hunted to extinction in
Europe, both for fur and for castoreum , a secretion from its scent
gland believed to have medicinal properties. However, the beaver is
now being re-introduced throughout Europe. Several thousand live on
NORTH AMERICAN BEAVER
North American beaver
The North American beavers prefer the (inner) bark of aspen and poplar but will also take birch, maple, willow, alder, black cherry, red oak, beech, ash, hornbeam and occasionally pine and spruce. They will also eat cattails , water lilies and other aquatic vegetation, especially in the early spring (and contrary to widespread belief, they do not eat fish).
These animals are often trapped for their fur. During the early 19th
century, trapping eliminated this animal from large portions of its
These trees, up to 250 mm (9.8 in) in diameter, were felled by beavers in one night.
The habitat of the beaver is the riparian zone , inclusive of stream
bed. The actions of beavers for hundreds of thousands of years in
The beaver works as a keystone species in an ecosystem by creating wetlands that are used by many other species. Next to humans, no other extant animal appears to do more to shape its landscape. Beavers potentially even affect climate change .
Beavers fell trees for several reasons. They fell large mature trees, usually in strategic locations, to form the basis of a dam, but European beavers tend to use small diameter