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The American Beaver
| Article
# : |
20715 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
9 / 1992 |
1,914 Words |
| Author
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Dwight G. Smith
Dwight G. Smith is professor and chairman of the biology
department at Southern Connecticut State University in New
Haven. His latest book, Plants, was released this summer by
Pearson Publishing Company of Boston. |
An animal architect famous for its ability to transform landscapes, the American beaver has a checkered history. The search for beaver--prized by the early European settlers for its prime pelt of thick, chestnut brown fur--stimulated the exploration of the American West and spawned the great fortunes of the John Jacob Astor and the Hudson Bay Company. Beaver were so intensively trapped that by the turn of the century they had been widely extirpated, occurring only in remote and inaccessible locales.
State and federal recovery efforts centering on reintroduction and protective legislation provided the basic framework for the successful reestablishment of beaver in many areas of the East, even in several heavily populated parts of New England.
Beaver are members of the single largest group of mammals, the order Rodentia. Their nearest rodent relatives include the squirrels, chipmunks, gophers, woodchucks, and the sewellel, or mountain beaver of the West. The beaver is the largest rodent in North America and one of the largest in the world, exceeded in size only by the capybara of Central and South America. Its scientific name is Castor Canadensis. Castor is a reference to the castoreum oil, obtained from the beavers' anal scent glands, which is used as a perfume fixative, while Canadensis refers to Canada--the location from which the first specimens were described. The American beaver originally ranged from Alaska and central Canada southward through most of the United States and into northern Mexico. Another species, Castor fiber, occurs in Eurasia, from northern Europe through eastern Siberia.
The beaver is a chunky, heavily built rodent, measuring some three plus feet in length and weighing between 60 and 70 pounds. Like all rodents, the beaver has a single pair of upper and lower incisors that are used for chewing or chipping. Beaver differ from most other rodents in their adaptations for an aquatic life. The beaver's large size and dense fur provide protection against cold, northern waters. Their hind feet are prominently webbed for swimming. Split inner toes on each hind foot are used to comb oil over the fur. Both the nostrils and ears have valves that close when the beaver is underwater, while the eyes are protected by a thin, filmy, nictitating membrane. Their lips seal around and behind the incisors to enable the beaver to work underwater, cutting saplings or maneuvering cut branches and twigs into their dam or lodge. The broad, flat, and scaly tail serves as a rudder when swimming or may be slapped sharply on the water surface to warn of danger. The paddle-shaped tail can also be used as a
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