Stop cutting down

The beaver (genus Castor) is a primarily nocturnal, large, semiaquatic rodent. Castor includes two extant species, the North American beaver (Castor canadensis) (native to North America) and Eurasian beaver (Castor fiber) (Eurasia).[1] 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.[2] Contents [hide] 1General 2Etymology 3Species 3.1Eurasian beaver 3.2North American beaver 4Habitat 4.1Dams 4.2Lodges 4.3Water quality and beavers 4.4Urban beavers in United States 4.5As an introduced non-native species 5Social behavior 5.1Family life 5.2Territories and spacing 6Commercial uses 6.1Trapping 7In culture 7.1As a national emblem 7.2In dietary law 7.3In computer science 8References 9Further reading 10External 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, and many species of giant beaver existed until quite recently, such as 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.[3][4] 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.[5] 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.[6] 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.[7] 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 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 bibar, the Old Norse bjorr, the Middle Dutch and Dutch bever, the Low German bever, the 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.[8] Species 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.[9] 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 and a female European resulting in a single stillborn kit. These factors make interspecific breeding unlikely in areas where the two species' ranges overlap.[9] 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 and the Rh"ne and in parts of 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),[10] Bavaria, Austria, Netherlands, Serbia (Zasavica bog), Denmark (West 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 to