The New International Encyclopædia/Beaver

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BEA′VER (AS. beofer, Ger. Biber, OCh. Slav. bebrŭ, Skt. babhrus, large ichneumon, also ‘brown’; to this latter root the word may possibly ultimately belong). A large aquatic rodent of the family Castoridæ, remarkable for its constructive habits, and yielding a valuable fur and the substance castoreum. The family includes only one species, in the opinion of the majority of naturalists, which is, or has been, distributed throughout most of the forested parts of the North Temperate Zone. To this species Linnæus gave the name Castor fiber, and the American form has been regarded as merely a variety of it. Recent American specialists, like Rhoads (Proc. Am. Philos. Soc., 1898), believe, nevertheless, that the American beaver is specifically different from that of the Old World, is entitled to the name Castor Canadensis, and is divisible into three distinct local races. In general characteristics all beavers agree so closely, however, that these niceties of classification may be left to the taxonomists.

The Old World Beaver, once widely common throughout Europe and Northern Asia, is now rare and isolated. Extinct in the British Isles since the Twelfth Century, a few colonies are preserved in the parks of the Marquis of Bute and other noblemen. It is said to exist in southeastern Norway, and isolated, pairs are occasionally seen on some of the large German rivers, and in Austria, under protection of great landowners, “They also occur sparingly in Russia and Poland, in the streams of the Ural Mountains, and in those which flow into the Caspian. They live in burrows on the banks of rivers, like the water-rat, and show little of the architectural instinct so conspicuous in the American form; but this may be owing to unfavorable external conditions rather than to want of the faculty, for there is a well-authenticated instance of a colony of beavers, on a small stream near Magdeburg, whose habitations and dam were exactly similar to those found in America.” In Siberia they still exist in considerable numbers, though their pelts do not now figure largely in the export of furs, and there the animal is inclined to erect lodges and dams.

The American Beaver was scattered primitively over all wooded North America, from Mexico to Labrador and the northwestern limit of tree-growth. It has been banished from all the more thickly settled parts, but survives in greater or less numbers throughout Canada north of civilized Ontario and Quebec, in the Rocky Mountain and Californian ranges, in the Appalachians south of West Virginia, and along the borders of northwestern Mexico. It is steadily decreasing, however, even in the Hudson Bay region. The beaver is usually at least 2 feet in length from the nose to the root of the tail, and weighs about 35 pounds, and the tail is about 10 inches in length. These dimensions are sometimes exceeded. The general form of the animal is thick and clumsy, broadest at the hips and squirrel-like. The body terminates in a thick oval tail, flattened transversely, about twice as long as broad, and naked of hairs, the surface being covered with plates of black, indurated skin, resembling horn-scales. The fore limbs are small and squirrel-like, the hinder ones large and powerful. Each foot has 5 toes; those of the fore-feet are short, and not connected by a web; those of the hind feet are long, spreading out like the toes of a goose, and webbed to the nails. In accordance with this remarkable peculiarity, the beaver in swimming makes use of the hind feet alone, the fore-feet remaining motionless and close to the body. The tail is of service as a sculling-oar and a rudder, and its loud slapping of the water when an alarmed animal dives is an effective signal of danger to others. The head is thick and broad, the nose obtuse, the eyes small, the ears short and rounded. The incisor or cutting teeth (two in each jaw) exhibit in the highest perfection this cardinal characteristic of the Rodentia. They are formed in front of hard, orange-colored enamel, while the back of the tooth is formed of a softer substance, more easily worn down, so that a sharp, chisel-like edge is always preserved; the bulbs being also persistent, so that the teeth are continually growing as they are worn away. There are four flat molar teeth (or grinders) on each side in each jaw.

NIE 1905 Beaver - skull.jpg


Showing the chisel-like incisors.

The fur consists of two kinds, the longer hair comparatively coarse, smooth, and glossy; the under coat dense, soft, and silky. The color is generally chestnut, rarely black, spotted, or nearly white. The largest and reddest beavers are those dwelling on the streams of the northern Pacific Coast, the smallest and darkest those of the Hudson Bay region, while those inhabiting the southern Alleghanies are reddish brown, and those of the southern Rockies are pale. In consequence of its aquatic and bark-eating habits, the beaver is limited to the neighborhood of streams and ponds in wooded districts, and the northern range of the species is everywhere terminated by the limits of the forest growth. Its extraordinary powers of gnawing are exerted to cut down trees several inches in diameter, both for food and for the construction of those houses and dams which have rendered it so much an object of admiration to mankind. Dr. Elliott Coues mentions a poplar cut by beavers on the Upper Missouri, which he found to be 9 feet in circumference at the point of attack; but this was exceptional. This cutting is accomplished by the animals standing upon their hind feet and gnawing in parallel lines across the grain, then wrenching or biting out the chip between, and so steadily deepening the cut. The assertion that they can or do cause trees to fall in any desired direction is not justified by facts. Large trees are usually felled by the united efforts of a family of beavers.

Community Life and Architecture.—The architectural operations and coöperative life of these animals are very wonderful, although the statement, at one time commonly made, that beavers drive stakes into the ground, has no foundation in fact; and some of the other particulars which passed current along with it were equally fabulous. They dwell normally in colonies along streams, which may have been inhabited for scores of generations, and whose improvements represent the combined labor of thousands of individuals past and present. Such a colony begins by the settlement in the spring upon some sluggish, moderately deep woodland stream or pond of a pair of young beavers, who have emigrated thither from some old colony. Their first labor is to dig a burrow in the bank, the entrance to which is at a safe depth beneath the water, and the interior chamber at a safe height above its normal rise. In this burrow they make their home the first year, or perhaps two years; and such burrows, more or less in use and serving as refuges in danger, are common always in beaver settlements. It is essential that a sufficient depth of water be maintained before the door of this burrow to give clear ingress and egress under the winter's ice, and to afford room for storage of winter provisions; and in most places chosen by the animals this can be arranged only by damming the stream. As the droughts and low water of summer begin, therefore, the beavers seek a place in the stream a little below their residence, where it is narrow, not more than 2½ feet deep, and has a firm bottom, and begin a dam. Gnawing down saplings 10 or 12 feet long, they drag and float them to the spot, and sink them lengthwise, side by side, across the current, beginning at the centre of the channel and loading them with stones, sods, and mud, to keep them in place. They will handle remarkably large stones for this purpose. The work is gradually extended until it reaches the bank on each side, and in doing so a convex outline upstream is usually given; but this probably is an accident of the increasing pressure of the obstructed current on the progressing wings of the new dam rather than an engineering design, for reverse (or weak) curves are frequently seen. Such a dam grows constantly by the addition of all sorts of material—not only the logs and sticks from which the bark has been gnawed for food, but others cut for the purpose, and a constant intermixture of roots and branches with stones, moss, grasses, and mud.

Additions, as well as constant repairs, are made on the upper side, which comes to present a low slope and comparative solidity, while the lower front of the dam is a more abrupt tangle of sticks and branches. The beavers work at the dam only at night, except in an emergency, and each one does what it thinks proper in a quite independent way, though the result is for common benefit. After many years such dams may be 4 or 5 feet high at the channel, and stretch to the right and left across low ground for 50 yards or more, converting the space above it into a broad, grassy pond, having a network of clear channels. Morgan describes dams 600 feet long in northern Wisconsin, with many acres of flooded ground. The water does not flow over the tops of these dams, but percolates through them, though some of them become seemingly solid barriers of earth. “In places,” says 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 water and ice; 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.” A large proportion of the marshy ponds and peat-bogs of the country have had this origin.

Meanwhile, from the first summer onward, the gradually increasing number of beaver families have built each for itself permanent homes, known from their resemblance to the Algonkian wigwam as ‘lodges.’ The sites chosen are along the banks of the stream or canal, and several houses may be so close together as to touch, or they may be widely scattered. The larger lodges are, in the interior, about 7 feet in diameter, and between 2 and 3 feet high, with the floor and inner walls made smooth by gnawing and wear. The entrances are always two, both leading down into the water, and in northerly regions there is no opening into the air—a needful precaution against the cold of mid-winter, as well as against such insidious foes as weasels and blacksnakes. This structure, like the dam, is formed of branches of trees, matted with mud, grass, moss, and other material. The walls are very thick, and the entire structure not only secures much warmth, but is an efficient protection from wolves, wolverines, and other beasts of prey, especially when solidly frozen in winter. Each family builds, maintains, and occupies its own lodge, the current belief that several families live together arising from the fact that the young beavers usually continue to live with their parents until the third year. Single ‘bachelors’ dwelling remote and alone are occasionally seen.

Food and Winter Provision.—The food of beavers is almost wholly the bark of deciduous trees, especially poplar, birch, willow, linden, and maple; they never eat ‘evergreen’ bark, and are absent from forests exclusively coniferous. In the summer they gnaw at fresh bark day by day, and also eat more or less of lily-roots and other green vegetables, berries, and leaves. The impossibility of obtaining this food in winter, when the waters and woods are clogged with ice and snow, compels them to prepare a supply. For this purpose the beavers become very active in the autumn, each family cutting down large trees and gnawing their limbs and trunks into sections small enough to be dragged to the water and floated to the neighborhood of their lodge. There this material is sunk to the bottom and firmly anchored (in a manner not comprehended), until a sufficient supply has been acquired. The dams are also especially repaired in autumn. The freezing of the stream puts an end to their labors, whereupon the beavers retire to their lodges and remain there, subsisting upon their store, pieces of which are daily taken into the house, or into some bank burrow, and the bark is eaten.

It will readily be seen that the supply of edible wood within a manageable distance from the water would soon be exhausted by a beaver colony, and perhaps the most important service of the dam and its pond is to provide against this contingency. In a flat country the mere raising of the water by flooding spaces of woods answers the purpose to some extent; but this is most intelligently supplemented by the animals, who dig deep canals, 2 or 3 feet wide, which penetrate the woods in various directions, sometimes for 100 yards or more, and thus render accessible a large number of trees otherwise out of reach. These canals are kept open with great pains, while the rest of the pond becomes gradually grown up with grass, and they form avenues along which lodges and burrows are placed, and where the colony may swim freely, and float their food and building materials from the woods to their lodges and dams, of which latter, on a long-tenanted and favorable stream, several may exist. This perfection of beaver economy is by no means seen everywhere, but might commonly be observed previous to 1850 in such highly favorable regions as the swampy forests about the headwaters of the Mississippi, and it is being renewed in northern Maine, where, under the protection of law, beavers are increasing and reoccupying their ancient haunts.

Economic Considerations.—Beavers are closely related to the squirrels, and, like them, ‘sit up’ a great deal, holding their food up to their mouths in their fore paws, which otherwise are used very dexterously. It is needless to contradict the many foolish stories as to the use of the tail as a vehicle for carrying mud, a trowel for applying it, and so on. The animals live well in confinement, and colonies are nourishing in zoölogical gardens and parks in New York, Washington, and other American cities, as well as abroad, where small, watered valleys, fenced with wire, are devoted to them. In closer captivity they betray their constructive instincts by weaving the sticks supplied them into the bars of their cages. They have usually four young at a birth, and keep them at home for two years.

The fur of the beaver, by reason of its softness and density, is one of the most valuable yielded by any animal, and in former times was the staple of the fur trade, especially in America, when the early prosperity of Canada and New York was based upon it. (For statistics see Furs and the Fur Trade.) It is probable that only the invention of silk-plush applied to the making of hats saved the animal from extinction long ago. Beavers were obtained mainly by wasteful methods of trapping, and they are so obtained yet, and chiefly in winter. Their nocturnal habits and extreme shyness make the shooting of them impracticable. Their flesh is esteemed by the Indians and frontiersmen.

Large glandular pouches, two in number, closely connected with the organs of reproduction, contain the substance called castoreum (q.v.). Its uses in the animal economy are by no means well known; they are probably analogous to those of musk and civet, but its peculiar pungent odor is so attractive to beavers that use is made of it as a bait for beaver-traps.

The beaver family dates from the middle of the Tertiary period, a fossil species of very large size occurring in the Upper Pliocene of Europe. Fossils of a small size and some distinctive peculiarities are found in the Miocene of the United States.

Bibliography. Consult: Harting, British Animals Extinct Within Historic Times (London, 1880); Morgan, The American Beaver and His Works (Philadelphia, 1868—illustrated); H. T. Martin, Castorologia (Montreal, 1892—illustrated); standard works (see Mammal). Compare Coypu.


NIE 1905 Beaver.jpg
1. COYPU (Myopotamus coypu), carrying young.     2. BEAVER (Castor canadensis) and house.
3. MUSKRAT (Fiber zibethicus), and winter lodge.