Beaver

Обыкновенный бобр, или речной бобр — полуводное млекопитающее отряда грызунов; один из двух современных представителей семейства бобровых (наряду с канадским бобром, которого ранее считали подвидом). Самый крупный грызун фауны Старого Света и второй по величине грызун после капибары.

The word "beaver" is inherited from the primo-European language (cf. Biber, the Bebros), is formed by incomplete doubling of the name of the brown color. The reconstructed base * bhe-bhru-. According to authoritative linguistic sources, the word beaver should be used in the meaning of an animal from a detachment of rodents with valuable fur, and the beaver in the meaning of the fur of this animal: a beaver collar, clothing on a beaver fur. However, in the colloquial language, the word beaver is universally used as a synonym for the word beaver (like a fox and a fox, a ferret and a choir).

The beaver is a large rodent adapted to a semi-aquatic life. The length of his body reaches 1-1,3 m, the height in the shoulder - up to 35,5 cm, and the mass - up to 30-32 kg. Sexual dimorphism is poorly expressed, females are larger. The body of the beaver is squat, with shortened 5-limbs; The posterior ones are much stronger than the anterior ones. Between the fingers there are swimming membranes, strongly developed on the hind limbs and slightly - on the forelegs. Claws on paws are strong, flattened. Claw II fingers of the hind limbs bifurcated - they beaver combs the fur. Tail paddle, strongly flattened from top to bottom; Its length - up to 30 cm, width - 10-13 cm. Hair on the tail is only at its base. Most of it is covered with large horny shields, between which grow rare, short and stiff hairs. Above the middle line of the tail, a horn keel extends. The eyes of the beaver are small; The ears are wide and short, barely protruding above the level of fur. Ears and nostrils close under water, eyes are closed with blinking membranes. Root teeth usually do not have roots; Weakly isolated roots are formed only in individual old individuals. The incisors behind are isolated from the oral cavity by special outgrowths of the lips, which allows the beaver to gnaw underwater. In the karyotype of the common beaver 48 chromosomes (in the Canadian beaver - 40). The beaver possesses a beautiful fur, which consists of rough coarse hair and a very thick silky undercut. Coloring fur from light chestnut to dark brown, sometimes black. The tail and extremities are black. Moulting once a year, at the end of spring, but lasts almost until winter. In the anal region are paired glands, adipose and directly the beaver itself, which gives off a highly smelling secret - a beaver jet. The prevailing opinion about the use of fat wigs as lubrication of fur from wetting is erroneous. The secret of the adipose cells performs a communicative function, solely carrying information about the owner (sex, age). The smell of the beaver jet serves as a guide for other beavers about the border of the territory of the beaver settlement, it is unique, like fingerprints. The secret of the fatty joints used together with the jet allows longer keeping the beaver mark in the "working" state due to the oily structure, which evaporates much longer than the secret of the beaver jet.

In early historical times, the common beaver was distributed throughout the forest zone of Europe and Asia, but due to intensive production by the beginning of the 20th century, the beaver in the greater part of the range was practically exterminated. The current range of the beaver is largely the result of efforts to acclimatize and reintroduce. In Europe, it lives in the Scandinavian countries, the lower reaches of the Rhone (France), the Elbe basin (Germany), the Vistula basin (Poland), the forest and partly the forest-steppe zones of the European part of Russia. In Russia, the beaver also occurs in the northern Trans-Ural region. Disparate foci of habitat of the common beaver are in the upper reaches Yenisei, Kuzbass, Baikal, in the Khabarovsk Territory, in Kamchatka. In addition, it is found in Mongolia (the Uruungu and Bimen rivers) and in Northeast China (Xinjiang Uygur Autonomous Region).

In early historical times, beavers everywhere inhabited the forest, taiga and forest-steppe zones of Eurasia, along river floodplains reaching to the north to forest-tundra, and to the south - to semi-deserts. Beavers prefer to settle along the banks of slowly flowing rivers, old men, ponds and lakes, reservoirs, irrigation canals and quarries. Avoid wide and fast rivers, as well as ponds that freeze to the bottom in winter. For beavers, it is important to have tree-shrub vegetation from the soft hardwood along the banks of the reservoir, as well as the abundance of water and coastal herbaceous vegetation that makes up their diet. Beavers swim and dive superbly. Larger lungs and the liver provide them with such air and arterial blood reserves that under water, beavers can remain 10-15 minutes, passing through this time to 750 m. On land, beavers are rather clumsy.

Beavers live alone or in families. A complete family consists of 5-8 individuals: a couple and young beavers - the offspring of the past and current years. The family site is sometimes occupied by the family for many generations. A small reservoir is occupied by one family or a single beaver. On larger reservoirs, the length of the family plot along the coast ranges from 0,3 to 2,9 km. From water, beavers are rarely removed more than 200 m. The length of the plot depends on the amount of feed. In areas rich in vegetation, plots can touch and even intersect. The borders of its territory beavers are marked with the secret of musk glands - a beaver stream. The labels are placed on special mounds of mud, mud and branches of 30 height and a width of up to 1 m. Beavers communicate with each other using odor marks, poses, tail punching over the water and shouts resembling a whistle. In danger, the floating beaver loudly flaps its tail on the water and dives. Cotton serves for all beavers within an audible alarm. Beavers are active at night and at dusk. In the summer, they leave the dwelling at dusk and work until 4-6 hours of the morning. In autumn, when the harvesting of feed for the winter begins, the work day is extended to 10-12 hours. In winter, activity decreases and shifts during the daytime; At this time of year on the surface of the beavers are almost not shown. At a temperature below? 20 ° C, the animals remain in their homes.

Beavers live in burrows or huts. The entrance to the beaver's home is always under water. The burrows dig holes in steep banks; They are a complex labyrinth with 4-5 inputs. Walls and ceiling burrows are carefully leveled and tamped. The living chamber inside the hole is arranged at a depth of not more than 1 m. The width of the living chamber is slightly more than a meter, the height is 40-50 centimeters. The floor is necessarily located at 20 centimeters above the water level. If the water rises in the river, the beaver raises the floor and scrays the earth from the ceiling. Sometimes the ceiling of the burrow collapses and in its place a deck of twigs and brushwood is arranged, turning the burrow into a transitional type of shelter - a half-hatch. In the spring, in the flood, beavers build leopards from branches and twigs on top of bushes with a bed of dry grass. Huts are built in places where burrowing holes is impossible, on low bogged banks and on shallows. The construction of new housing beavers rarely begin before the end of August. The huts have the appearance of a cone-shaped pile of brushwood, bound with mud and earth, up to 1-3 m in height and up to 10-12 m in diameter. The walls of the hut are carefully smeared with mud and clay, so that it turns into a real fortress unapproachable for predators; Air comes through the ceiling. Despite the widespread opinion, beavers apply clay with the help of the front paws, and not the tail (the tail serves exclusively as a rudder). Inside the hut there are lazy in the water and a platform towering above the water level. With the first frosts, beavers additionally isolate the huts with a new layer of clay. In winter, the huts hold a plus temperature, the water does not freeze in the manholes, and the beavers have the opportunity to enter the under-ice thickness of the reservoir. In severe frosts over the huts is the steam, which is a sign of habitation habitation. Sometimes in one settlement of beavers there are also huts and burrows. Beavers are very clean, never clog their homes with the remains of food and feces.

In water bodies with varying levels of water, as well as on small streams and rivers, beaver families build their famous dams (dams). This allows them to raise, maintain and regulate the water level in the reservoir. The dams are built below the beaver town from tree trunks, twigs and brushwood, fastened with clay, silt, pieces of alloy and other materials that beavers bring in the teeth or forepaws. If the reservoir has a fast current and there are stones on the bottom, they are also used as building material. Weight of stones can reach 15-18 kg. To build a dam, the places where the trees grow closer to the edge of the shore are selected. Construction begins with the fact that the beavers vertically stuck into the bottom of the branches and trunks, strengthening the gaps with branches and reeds, filling the cavities with mud, clay and stones. As a supporting frame, they often use a tree fallen into a river, gradually overlaying it from all sides with building material. Sometimes the branches in the beaver dams take root, giving them additional strength. The usual length of the dam is 20-30 m, the width in the base is 4-6 m, at the ridge - 1-2 m; Height can reach 4,8 m, although usually - 2 m. The old dam easily withstands the weight of a person. The record in the construction of dams belongs, however, not ordinary, and Canadian beavers - a dam built by them on the river. Jefferson (Montana), reached a length of 700 m. The shape of the dam depends on the speed of the current - where it is slow, the dam is practically straight; On the fast rivers it is curved in the direction of the current. If the current is very strong, higher on the river, the beavers erect small additional dams. In the dam is often arranged a drain, so that it does not break through the flood. On average, to build an 10 m dam, the beaver family takes about a week. Beavers carefully monitor the safety of the dam and patch it in the event of a leak. Sometimes in the construction involves several families working in shifts.

The Swedish ethologist Wilson (1971) and the French zoologist Richard (1967, 1980) contributed greatly to the study of the behavior of beavers in the construction of dams. It turned out that the main stimulus to construction is the noise of running water. Possessing an excellent hearing, the beavers unmistakably determined where the sound changed, which means that the structure of the dam has changed. In this case, they did not pay attention even to the lack of water - in the same way, the beavers reacted to the sound of water recorded on the tape recorder. Further experiments have shown that sound, apparently, is not the only stimulus. So, a pipe laid through a dam, beavers hammered with silt and branches, even if it passed on the bottom and was "inaudible". At the same time, it remains unclear how the beavers distribute duties among themselves in collective work. For the construction and harvesting of forage, the beavers bring down trees, biting them at the base, chewing off the branches, then dividing the trunk into parts. The axle is 5-7 in diameter and the beaver is pounding for 5 minutes; A tree with a diameter of 40 cm knocks and cuts overnight, so that by morning on the site of the animal's work there is only a stubble stump and a bunch of shavings. The trunk of a beaver with a beaver burr takes on the characteristic shape of an hourglass. The beaver gnaws, rising to its hind legs and leaning on its tail. His jaws act like a saw: in order to dump a tree, the beaver rests on the upper incisors in its cortex and starts to swiftly drive the lower jaw from side to side, making 5-6 movements per second. The incisors of the beaver are self-sharpening: only their front side is covered with enamel, the back consists of less solid dentin. When the beaver gnaws anything, the dentin is soiled faster than the enamel, so the front edge of the tooth remains sharp all the time. Some of the branches of the fallen tree are eaten away by the beavers, others are demolished and towed or floated along the water to their home or to the site of the construction of the dam. Every year, walking the same routes for food and building materials, they trample on the shore paths that are gradually flooded with water - beaver canals. On them they fuse the woody forage. The length of the canal reaches hundreds of meters with a width of 40-50 cm and a depth of up to 1 m. Beavers always keep the canals clean.

Beavers are strictly herbivorous. They feed on bark and shoots of trees, preferring aspen, willow, poplar and birch, as well as various herbaceous plants (water lily, egg, iris, cattail, reed, etc., up to 300 names). The abundance of softwood trees is a necessary condition for their dwelling. The hazel, linden, elm, bird cherry and some other trees are of secondary importance in their diet. Alder and oak do not eat, but they are used for buildings. The daily amount of food is up to 20% of the weight of the beaver. Large teeth and a powerful bite allow the beaver to easily cope with hard plant foods. The cellulose-rich food is digested with the participation of the microflora of the intestinal tract. Usually the beaver consumes only a few species of trees; To switch to a new diet, he needs an adaptation period, during which the microorganisms adapt to the new diet. In summer, the proportion of herbaceous feed in the diet of beavers increases. In the autumn, beavers are engaged in harvesting wood forage for the winter. Stocks of beavers are put in water, where they keep their nutritional quality until February. The volume of reserves is huge - up to 60-70 cubic meters per family. To ensure that the food does not freeze into ice, beavers usually podtaplivayut it below the water level under steep overhanging banks. Thus, even after the pond freezes, food remains available to beavers under the ice.

Beavers are monogamous, the female dominates. Offspring bring 1 once a year. The mating season lasts from mid-January to the end of February; Mating occurs in water under ice. Pregnancy lasts 105-107 days. Cubs (1-6 in brood) will be born in April-May. They are half-blind, well-pubescent, weigh an average of 0,45 kg. Through 1-2 days they can already swim; The mother teaches the beaver, literally pushing them into the underwater corridor. At the age of 3-4 weeks, the Bobryats switch to eating leaves and soft stems of herbs, but the mother continues to feed them with milk until 3 months. Adult young growth usually does not leave 2 for a year. Only in 2 year young beavers reach sexual maturity and are resettled. In captivity, the beaver lives up to 35 years, in nature 10-17 years.