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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) ( Eurasia
Eurasia
). Beavers are known for building dams, canals, and lodges (homes). They are the second-largest rodent in the world (after the capybara ). Their colonies create one or more dams to provide still, deep water to protect against predators, and to float food and building material. The North American beaver population was once more than 60 million, but as of 1988 was 6–12 million. This population decline is the result of extensive hunting for fur, for glands used as medicine and perfume, and because the beavers' harvesting of trees and flooding of waterways may interfere with other land uses.

CONTENTS

* 1 General * 2 Etymology

* 3 Species
Species

* 3.1 Eurasian beaver * 3.2 North American beaver
North American beaver

* 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

GENERAL

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 Eocene
Eocene
, and many species of giant beaver existed until quite recently, such as Trogontherium
Trogontherium
in Europe, and Castoroides in North America.

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.

ETYMOLOGY

The English word "beaver" comes from the Old English
Old English
word beofor or befer (recorded earlier as bebr), which in turn sprang from the Proto-Germanic root *bebruz. Cognates in other Germanic languages include the Old Saxon
Old Saxon
bibar, the Old Norse
Old Norse
bjorr, the Middle Dutch and Dutch bever, the Low German
Low German
bever, the Old High German
Old High German
bibar and the Modern German Biber. The Proto-Germanic word in turn came from the Proto-Indo-European (PIE) word *bhebhrus, a reduplication of the PIE root *bher-, meaning "brown" or "bright", whose own descendants now include the Lithuanian bebras, the Czech bobr and the Welsh befer, as well as the Germanic forms.

SPECIES

North American beaver
North American beaver
tracks

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
North American beaver
and a female European resulting in a single stillborn kit. These factors make interspecific breeding unlikely in areas where the two species' ranges overlap.

EURASIAN BEAVER

Main article: Eurasian beaver A Eurasian beaver

The 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 the Elbe
Elbe
and the Rhône and in parts of Scandinavia
Scandinavia
. A thriving community lives in northeast Poland, and the Eurasian beaver also returned to the Morava River banks in Slovakia and the Czech Republic. They have been reintroduced in Scotland ( Knapdale
Knapdale
), Bavaria
Bavaria
, Austria, Netherlands, Serbia (Zasavica bog), Denmark (West Jutland
Jutland
) and Bulgaria and are spreading to new locations. The beaver became extinct in Great Britain in the sixteenth century: Giraldus Cambrensis reported in 1188 (Itinerarium ii.iii) that it was to be found only in the Teifi in Wales and in one river in Scotland, though his observations are clearly second hand. In 2001, Kent Wildlife Trust successfully introduced a family of beavers at Ham Fen, the last remaining ancient fenland in the county close to the town of Sandwich ; these are now established and are breeding. In October 2005, six Eurasian beavers were reintroduced to Britain in Lower Mill Estate in Gloucestershire
Gloucestershire
; in July 2007 a colony of four Eurasian beavers was established at Martin Mere in Lancashire, and a small population of probably Eurasian beavers is being monitored in Devon. A trial re-introduction occurred in Scotland in May 2009. Feasibility studies for a reintroduction to Wales are at an advanced stage and a preliminary study for a reintroduction of beavers to the wild in England has recently been published.

NORTH AMERICAN BEAVER

Main article: North American beaver
North American beaver
A North American beaver
North American beaver
Surprised by a major snow melt, a beaver had to start its cut all over again

The North American beaver
North American beaver
(Castor canadensis), also called the Canadian beaver (which is also the name of a subspecies), American beaver, or simply beaver in North America, is native to Canada, much of the United States and parts of northern Mexico. This species was introduced to the Argentine and Chilean Tierra del Fuego, as well as Finland, France, Poland and Russia.

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 original range. Beaver
Beaver
furs were used to make clothing and top-hats. Much of the early exploration of North America was driven by the quest for this animal's fur. Native peoples and early settlers also ate this animal's meat. Through trap and transfer and habitat conservation , beavers made a nearly complete recovery by the 1940s. The current beaver population has been estimated to be 10 to 15 million; one estimate claims that there may at one time have been as many as 90 million.

HABITAT

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 Northern Hemisphere
Northern Hemisphere
have kept these watery systems healthy and in good repair.

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