|
The North American beaver (''Castor canadensis'') is one of two extant beaver species. It is native to North America and introduced to Patagonia in South America and some European Countries (e.g., Norway). In the United States and Canada, the species is often referred to simply as "beaver", though this causes some confusion because another distantly related rodent, ''Aplodontia rufa'', is often called the "mountain beaver". Other vernacular names, including American beaver and Canadian beaver, distinguish this species from the other extant beaver species, ''Castor fiber'', which is native to Eurasia. The North American beaver is the national animal of Canada.〔http://members.shaw.ca/kcic1/beaver.html〕 ==Description== This beaver is the largest rodent in North America and competes with its Eurasian counterpart, the European beaver, for being the second-largest in the world, both following the South American capybara. Adults usually weigh from , with being typical. The head-and-body length is , with the tail adding a further . Very old individuals can exceptionally exceed normal sizes, weighing more than or even as much as .〔(【引用サイトリンク】title=Home Page, Alaska Department of Fish and Game )〕〔(The Beaver – Life Tracks ). Timberwolfinformation.org〕〔Burnie D and Wilson DE (Eds.), ''Animal: The Definitive Visual Guide to the World's Wildlife''. DK Adult (2005), ISBN 0789477645〕〔Boyle, Steve and Owens, Stephanie (February 6, 2007) (North American Beaver (''Castor canadensis''): A Technical Conservation Assessment ). USDA Forest Service, Rocky Mountain Region〕 Like the capybara, the beaver is semi-aquatic. The beaver has many traits suited to this lifestyle. It has a large flat paddle-shaped tail and large, webbed hind feet. The unwebbed front paws are smaller, with claws. The eyes are covered by a nictitating membrane which allows the beaver to see underwater. The nostrils and ears are sealed while submerged. A thick layer of fat under its skin insulates the beaver from its cold water environment. The beaver's fur consists of long, coarse outer hairs and short, fine inner hairs (see Double coat). The fur has a range of colours but usually is dark brown. Scent glands near the genitals secrete an oily substance known as castoreum, which the beaver uses to waterproof its fur. Before their near-extirpation by trapping in North America, beaver were practically ubiquitous and lived from the arctic tundra to the deserts of northern Mexico, and from the Atlantic to the Pacific Oceans. Physician naturalist Edgar Alexander Mearns' 1907 report of beaver on the Sonora River may be the southernmost extent of the range of this North American aquatic mammal. However, beaver have also been reported both historically and contemporaneously in Mexico on the Colorado River, Bavispe River and San Bernardino River. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「North American beaver」の詳細全文を読む スポンサード リンク
|