|Beavers are semi-aquatic rodents native to North America and Europe. They are the only living 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 continue to grow throughout life. Adult specimens weighing over 25 kg (55 lb) are not uncommon. Beavers living along rivers and streams linked to the salt water sections of the Gulf of St. Lawrence, Canada weigh over 30 kg (66 lbs), which biologist attribute to the salt water vegetation found in these habitats. Females are as large as or larger than males of the same age, which is uncommon among mammals.
Species: C. canadensis, C. fiber, C. californicus
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. This disruption is not limited to human geography; beavers can destroy nesting habitat for endangered species, and often destroy mature trees for which they have no use.
On the other hand, dam building is extremely beneficial in restoring wetlands. 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. Over the eons, this collection of silt produces the rich bottom land so sought after by farmers. Beaver dams also reduce erosion as well as decrease the turbidity that is a limiting factor for much aquatic life. While beavers can create damage, part of the problem is one of perception and time scale. Such damage as the undermining of a roadway or the drowning of some trees is very visible shortly after the beginning of beavers' activity in an area. The benefits, mentioned below, are long-term and not easily seen except by someone who is monitoring a catchment and realizes the beneficial effects of beaver dams.
As the wetland fills and dries out, pasture species colonize it and it becomes a meadow suitable for grazing. In an area with nothing but forest down to the stream edge, this provides a valuable niche for many animals which otherwise would be excluded.
Finally the meadow will be colonized by riverine trees, typically aspens, willows and such species which are favored by the beaver. Beavers are then likely to recognize the area, and the cycle begins again.
As related above, each time this process repeats itself another layer of rich organic soil is added to the bottom of the valley. The valley slowly fills and the flat area at the bottom gets wider. Research is sparse on this topic, but it seems likely that much of the fabled bottom land in North America was created, or at least added to, by the efforts of the generations of beavers that lived there.
Pesticide and herbicide removal
Both beaver testicles and castoreum, a bitter-tasting secretion with a slightly fetid odor contained in dried preputial or vaginal follicles of male or female beaver, have been articles of trade for use in traditional medicine. Yupik (Eskimo) medicine used dried beaver testicles like willow bark to relieve pain. Beaver testicles were exported from Levant (a region centered on Israel) from the tenth to nineteenth century. Claudius Aelianus comically described beavers chewing off their testicles to preserve themselves from hunters. European beavers (Castor fiber) were eventually hunted nearly to extinction in part for the production of castoreum, which as used as an analgesic, anti-inflammatory, and antipyretic. Castoreum was described in the 1911 British Pharmaceutical Codex for use in dysmenorrhea and hysterical conditions (i.e. pertaining to the womb), for raising blood pressure and increasing cardiac output. The activity of castoreum has been credited to the accumulation of salicin from willow trees in the beaver's diet, which is transformed to salicylic acid and has an action very similar to aspirin. Castoreum continues to be used in perfume production.
The following text is taken from the 1911 Encyclopedia
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 grayish color, the other much coarser and longer, and of a reddish brown.
Beavers are essentially aquatic in their habits, never traveling 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 neighborhood 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 favorite 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 odor, 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.
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