Beaver

? Beavers Fossil range: Late Miocene - Recent
American Beaver
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Rodentia Family: Castoridae Hemprich, 1820 Genus: Castor Linnaeus, 1758
Species
C. canadensis C. fiber

Beavers are semi-aquatic rodents native to North America and Europe. They are the only members of the family Castoridae, which contains a single genus, Castor. Genetic research has shown the European and North American beaver populations to be distinct species and that hybridization is unlikely.

Beavers are best known for their natural trait of building dams in rivers and streams, and building lodges in the eventual artificial pond. They are the second largest rodents, after the capybara. Beavers continue to grow throughout life. 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 in most species.

Species

The European Beaver (Castor fiber) was hunted almost to extinction in Europe, both for fur, and for castoreum, a secretion of its scent gland believed to have medicinal properties. However, the beaver is now being re-introduced throughout Europe. Several thousands live on the Elbe, the Rhone and in parts of Scandinavia. They have been reintroduced in Bavaria and The Netherlands and are tending to spread to new locations. The beaver finally 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 first hand.

In October 2005, six European beavers were re-introduced to Britain in Lower Mill Estate in Gloucestershire, and there are plans for re-introductions in Scotland and Wales. [1]

The American Beaver (C. canadensis) is the national animal of Canada; in fact, it is depicted on the Canadian five-cent piece and was on the first Canadian postage stamp, the Three Penny Beaver. However, in several areas of that country, it is considered a pest. The American Beaver is also the state animal of Oregon, the state mammal of New York (after the historical emblem of New Netherland) and the mascot of Oregon State University. It is also a common school emblem for engineering schools, including the California Institute of Technology and the Massachusetts Institute of Technology. It is also an emblem for London School of Economics and the name of its student newspaper - The Beaver.

The extinct North American Giant beaver (Castoroides ohioensis) was one of largest rodents that ever evolved. It disappeared, with other large mammals in the Holocene extinction event, about 10,000 years ago.

Dams

The dams are created both as a protection against predators, e.g., coyotes, wolves and bears, and to provide easy access to food during winter. It is both the sound of water in motion and the current that stimulates the beavers to build. If for example a pipe is placed under the dam to drain it the beavers may stuff it with a tree trunk unless the pipe inlet is protected with a large cage-like filter. They may repair any damage to the dam and build it higher as long as the sound is there, however, in times of high water, they often allow spillways in the dam to flow freely. Conversely, beavers will attempt to build dams in response to recordings of water flowing even in the absence of water.

The ponds created by well-maintained dams help isolate the beavers' home, their lodge, also created from severed branches and mud. The lodge has underwater entrances to make entry nearly impossible for any other animal (however, muskrats have been seen living inside beaver lodges with the beavers who made it).

Destroying a beaver dam without removing the beavers takes a lot of effort, especially if the dam is downstream of an active lodge. Beavers can rebuild such primary dams overnight, but may not defend secondary dams as vigorously.

Recent studies involving beaver habitual activities have indicated that beavers may respond to a array of stimuli, not just the sound of running water. In two experiments Wilson (1971) and Richard (1967, 1980) demonstrate that although beavers will pile material close to a loudspeaker emitting sounds of water running, they only do so after a considerable period of time. Additionally the beavers, when faced with a pipe allowing water to pass through their dam, eventually stopped the flow of water by plugging the pipe with mud and sticks. The beavers were observed to do this even when the pipe extended several meters upstream and near the bottom of the stream and thus produced no sound of running water.

Beaver dams can be disruptive; the flooding can cause extensive property damage, and when the flooding occurs next to a railroad roadbed, it can cause derailments by washing-out under the tracks, or when a beaver dam bursts and the resulting flash flood overwhelms a culvert.

Yet dam building activity restores wetlands, the land's most beneficial ecosystem. Such wetland benefits include flood control downstream, biodiversity (by providing habitat for many rare as well as common species), and water cleansing, both by the breakdown of toxins such as pesticides and the retention of silt by beaver dams. The latter also reduces erosion as well as decreasing turbidity that is the limiting factor for aquatic life.

When objectionable beaver flooding occurs, modern water level control devices can be installed for a cost-effective and environmentally sound solution (www.BeaversWW.org).

Danger signal

When startled or frightened, a swimming beaver will rapidly dive while forcefully slapping the water with its broad tail. This creates a loud 'slap', audible over large distances above and below water. This noise serves as a warning to other beavers in the area. Once a beaver has made this danger signal, all nearby beavers will dive and may not reemerge for some time.

Fur trade

Beaver pelts were used as barter by Native Americans in the 17th century to gain European goods. They were then shipped back to Great Britain and France where they were made into clothing items. Widespread hunting and trapping of beavers lead to their endangerment. Eventually, the fur trade fell apart due to declining demand in Europe and the take over of trapping grounds to support the growing agriculture sector.

Popular culture

Popular western culture typically depicts the animal positively, as a good natured and industrious character such as Mr. and Mrs. Beaver who are important heroic characters in the classic fantasy novel, The Lion, the Witch and the Wardrobe. Since the animal is a national symbol of Canada, the animal is a favourite choice for depicting Canadians as furry characters and was chosen to be the mascot of 1976 Summer Olympics held in Montreal with the name "Amik" ("friend" in Algonquin). The beaver's habits, habitat and conservation status (as of 1908) are recurring themes in The Tent Dwellers, by Albert Bigelow Paine. Due to their engineering capabilities, they also serve as the mascots of the Massachusetts Institute of Technology and the California Institute of Technology.

1911 encyclopedia text

Beaver, the largest European aquatic representative of the mammalian order RODENTIA, easily recognized by its large trowel-like, scaly tail, which is expanded in the horizontal direction.

The word is descended from the Aryan name of the animal, cf. Sanskrit babhru's, brown, the great ichneumon, Lat. fiber, Ger. Biber, Swed. bäver, Russ. bobr'; the root bhru has given "brown," and, through Romanic, "bronze" and "burnish."

The true beaver (Castor fiber) is a native of Europe and northern Asia, but it is represented in North America by a closely-allied species (C. canadensis), chiefly distinguished by the form of the nasal bones of the skull.

Beavers are nearly allied to the squirrels (Sciuridae), agreeing in certain structural peculiarities of the lower jaw and skull. In the Sciuridae the two main bones (tibia and fibula) of the lower half of the leg are quite separate, the tail is round and hairy, and the habits are arboreal and terrestrial. In the beavers or Castoridae these bones are in close contact at their lower ends, the tail is depressed, expanded and scaly, and the habits are aquatic.

Beavers have webbed hind-feet, and the claw of the second hind-toe double. They have poor eyesight, but a keen sense of hearing, smell, and touch.

In length beavers--European and American--measure about 2 ft. exclusive of the tail, which is about 10 inches long. They are covered with a fur to which they owe their chief commercial value; this consists of two kinds of hair--the one close-set, silky and of a greyish colour, the other much coarser and longer, and of a reddish brown.

Beavers are essentially aquatic in their habits, never travelling by land unless driven by necessity. Formerly common in England, the European beaver has not only been exterminated there, but likewise in most of the countries of the continent, although a few remain on the Elbe, the Rhone and in parts of Scandinavia. The American species is also greatly diminished in numbers from incessant pursuit for the sake of its valuable fur.

Beavers are sociable animals, living in streams, where, so as to render the water of sufficient depth, they build dams of mud and of the stems and boughs of trees felled by their powerful incisor teeth. In the neighbourhood they make their "lodges," which are roomy chambers, with the entrance beneath the water. The mud is plastered down by the fore-feet, and not, as often supposed, by the tail, which is employed solely as a rudder.

They are mainly nocturnal, and subsist chiefly on bark and twigs or the roots of water plants.

The dam differs in shape according to the nature of particular localities. Where the water has little motion it is almost straight; where the current is considerable it is curved, with its convexity towards the stream. The materials made use of are driftwood, green willows, birch and poplars; also mud and stones intermixed in such a manner as contributes to the strength of the dam; but there is no particular method observed, except that the work is carried on with a regular sweep, and that all the parts are made of equal strength.

"In places," writes Hearne, "which have been long frequented by beavers undisturbed, their dams, by frequent repairing, become a solid bank, capable of resisting a great force both of ice and water; and as the willow, poplar and birch generally take root and shoot up, they by degrees form a kind of regular planted hedge, which I have seen in some places so tall that birds have built their nests among the branches."

Their houses are formed of the same materials as the dams, with little order or regularity of structure, and seldom contain more than four old, and six or eight young beavers. It not unfrequently happens that some of the larger houses have one or more partitions, but these are only posts of the main building left by the builders to support the roof, for the apartments have usually no communication with each other except by water.

The beavers carry the mud and stones with their fore-paws and the timber between their teeth. They always work in the night and with great expedition. They cover their houses late every autumn with fresh mud, which, freezing when the frost sets in, becomes almost as hard as stone, so that neither wolves nor wolverines can disturb their repose.

The favourite food of the American beaver is the water-lily (Nuphar luteum), which bears a resemblance to a cabbage-stalk, and grows at the bottom of lakes and rivers. Beavers also gnaw the bark of birch, poplar and willow trees; but during the summer a more varied herbage, with the addition of berries, is consumed.

When the ice breaks up in spring they always leave their embankments, and rove about until a little before the fall of the leaf, when they return to their old habitations, and lay in their winter stock of wood. They seldom begin to repair the houses till the frost sets in, and never finish the outer coating till the cold becomes severe. When they erect a new habitation they fell the wood early in summer, but seldom begin building till towards the end of August.

Castoreum is a substance contained in two pear-shaped pouches situated near the organs of reproduction, of a bitter taste and slightly foetid odour, at one time largely employed as a medicine, but now used only in perfumery.

Fossil remains of beavers are found in the peat and other superficial deposits of England and the continent of Europe; while in the Pleistocene formations of England and Siberia occur remains of a giant extinct beaver, Trogontherium cuvieri, representing a genus by itself.