Bird class- warm-blooded animals, the body of which is covered with feathers (the only group of animals), and the forelimbs are turned into wings; hind limbs - legs. Birds fly beautifully, surpassing all other vertebrates in this respect. Also, birds move well on the ground, climb trees, many dive and swim in the water. Birds are extremely diverse in size, shape, color, habits and have adapted to living in various climatic conditions. There are about 9 thousand species.

External structure of a bird

Birds have a head, neck, torso, limbs and tail. The head of birds is small, it has a beak, eyes, nostrils. The beak is formed by bony jaws extended forward, which are covered from above with horny sheaths. Birds have no teeth, which makes the skull lighter. The nostrils are located at the base of the upper part of the beak. The rounded eyes are covered with two eyelids and a blinking membrane. Closer to the back of the head, the ear holes are hidden under the feathers. The movable neck connects the head to the compact body.

Features of the body structure of a bird

The most important orders of birds

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Sourse of information: Biology in tables and diagrams. / Edition 2e, - SPb .: 2004.

General characteristics. Birds - warm-blooded vertebrates from the group Amniota, adapted for flight. The forelimbs are modified into wings. The body is covered with feathers, which also form the supporting plane of the wings and tail. Part of the bones of the metatarsus and tarsus, merged, formed a single bone - the tarsus. The skull is articulated with the spine by one condyle. There is a cortex in the cerebral hemispheres, but their surface is smooth. The cerebellum is well developed. Lungs are spongy, connected to a system of air sacs. The heart is four-chambered. There is only the right aortic arch, the left one atrophies even during embryonic development. The organs of excretion are the pelvic kidneys. Fertilization is internal. They reproduce by laying eggs.

Currently, the Earth is home to about 9 thousand species of birds that inhabit all continents and islands. There are about 750 bird species in the USSR.

Modern birds are subdivided into three distinct supra-orders: (Carlnatae) , Keelless birds (Ra- titae), Penguins { linpennes).

Structure and vital functions. Appearance birds reflects their fitness for flight (Fig. 247). The body is streamlined, egg-shaped, compact. The neck of most birds is thin and flexible. On the head, a beak protrudes forward, consisting of a beak and a lower beak. For flight, the modified forelimbs are used - the wings. Most of their bearing plane is formed by large elastic flight feathers. The legs of birds take all the weight of the body, when moving on the ground, climbing trees, taking off and landing. The legs have four sections: thigh, lower leg, tarsus, and toes. Usually the bird's legs are four-toed, but sometimes their number is reduced to three or even two (African ostrich). Of the four fingers, in most cases, three are directed forward and one is directed backward.

Rice. 247. Outer (Field Harrier)

Veils. The skin of birds is thin, dry. The skin glands are absent. Only above the base of the tail in most birds is a special coccygeal gland, the secret of which is used to lubricate the feathers, which prevents them from getting wet. Feather cover is characteristic of birds. Feathers are common to all types of birds and are not found in other animals. Bird feathers evolved from the horny scales of reptiles.

Feather is a derivative of the skin epidermis (Fig. 248). It is formed by the horny substance - keratin. A single feather consists of a quill (a part immersed in the skin), a shaft and a fan.

Rice. 248. The structure of poultry nerms:

/ - rod; 2 - outer fan; 3 inner fan; ■ / - trunk; 5 - ochip; 6 "- full hole; 7 bow

Rice. 249. The structure of the bird's wing:

/ - brachial bone; 2 - elbow bone; 3 ...... the radius;

4 - the bone is po-zapyasgpan; 5 ......... part of the wrist; 6 ", 7

phalanges of the fingers; 8 - winglet; {.) pterygoid membrane; 10 - the bases of the flight feathers; // - primary flight feathers; 12 - secondary flight feathers

The rod is a dense corneal tube with a loose corneous core. The fan is formed by first-order barbs extending from the rod in both directions, from which, in turn, short second-order barbs extend. The beards of the second order bear small hooks that interlock the beards with each other, which is why an elastic light blade of the feather fan is formed. In delicate downy feathers, the shaft is shortened and bears thin delicate beards not interlocked by hooks. In fluff, the shaft is not developed and the barbs extend in a bundle from the common base.

Large elastic feathers that form the main part of the wing bearing plane are called flight feathers. Their fan is asymmetrical - the front side is narrow and the back side is wide. Such a structure allows the passage of air between the feathers when the wing is raised, and when the wing is lowered under air pressure, it causes a tight connection of the feathers. Larger flight feathers, resting on the bones of the wing, are called primary flight feathers, and smaller and less elastic feathers, connected to the bones of the forearm, "are secondary flight feathers (Fig. 249). Tail feathers that make up the tail and direct the flight of birds, They are distinguished by their large size, elasticity and asymmetry of the fans.The smaller feathers covering the body of birds are called contour, they give the body a streamlined shape.The areas on which they are located are called pterilias, and the areas of the skin without them are called apterias (Fig. 250). Apteria are located along the midline of the chest, in the axillary region, along the shoulder blades, that is, in those places of the body where the skin over the muscles strains during flight. Apterias are covered with adjacent contour feathers. In many birds, especially water birds, between the contour feathers down feathers and down are located, warming the body.

The role of feathers in the life of birds is large and varied. Flight and tail feathers form the majority of the wing and tail bearing surface and are therefore essential for flight. The feather cover gives the birds a streamlined shape, which facilitates their flight. Due to the high heat-shielding properties of feathers and air layers between them, the feather cover helps to preserve body heat in birds and, therefore, participates in thermoregulation of the body. It also protects the bird from various mechanical influences. A variety of feather pigments give birds a particular color, which is often patronizing.

Periodically, usually once or twice a year, the feather cover of birds is completely or partially renewed by molting; at the same time, old feathers fall out, and new ones develop in their place (sometimes of a different color). In most birds, plumage molt proceeds slowly and gradually, due to which they retain the ability to fly, but in waterfowl it proceeds so quickly that they temporarily cannot fly.

Rice. 250. Pterszhy and aptria birds (pigeon)

Rice. 251. The skeleton of a bird (dove):

/ - cervical vertebrae; 2 - thoracic vertebrae; 3 - tail vertebrae; 4
- coccygeal bone; 5, in-edges; 7 - sternum; S - keel; .V - blades; 10 - coracoid; // - clavicle (fork); 12
-- brachial bone; 13 - radius bone; 14- elbow bone; 15 -

metacarpus; 16 .....18 - phalanges of the fingers;

19 -21- pelvic bones; 22 - thigh bone; 23 - shin bone; 24 - tarsus; 25, 26 - phalanges of the fingers

The skeleton of birds is light and at the same time strong, which is important for flight (Fig. 251). Its lightness is achieved by the thinness of its constituent bones and the presence of cavities in the tubular bones of the forelimbs. The strength of the skeleton is largely due to the fusion of many bones.

The skull of birds is distinguished by a large thin-walled cerebral box, huge eye sockets, and toothless jaws. In adult birds, the bones of the skull are completely fused, which ensures its strength. The skull is articulated with the first cervical vertebra by one condyle.

The cervical vertebrae, the number of which varies in different birds, are articulated with each other by saddle-shaped articular surfaces, which gives the neck more flexibility. The thoracic vertebrae in adult birds are spliced ​​together. The ribs are attached with the lower ends to the sternum; at the posterior edge, they have hook-shaped processes, which overlap the ends of the ribs of the next pair; this gives the chest strength. The sternum of birds, with the exception of those that have lost the ability to fly, carries a high bone keel on the front surface, to which powerful pectoral and subclavian muscles are attached on both sides, which set the wing in motion.

The posterior thoracic, lumbar, sacral and - anterior caudal vertebrae in adult birds grow together with each other and with the thin iliac bones of the pelvis into a single sacrum, which serves as a solid base for the legs. The posterior caudal vertebrae merge to form the coccygeal bone, which looks like a vertical plate. It serves as a support for the tail feathers.

The shoulder girdle consists of three pairs of bones: saber-shaped shoulder blades, lying along the spine; swampy clavicles, which grow together with the lower ends into a fork, expanding the base of the wings; coracoids - massive bones connected at one end with the shoulder blades and bases of the humerus, and at the other with the sternum.

The wing skeleton consists of a large, hollow inside the shoulder bone, two bones (ulna and radial) of the forearm, a number of fused bones of the wrist and metacarpus and highly reduced and altered phalanges of II, III and IV fingers, I and V fingers are atrophied, II has only one phalanx , which serves as a support for a separate tuft of feathers on the outer edge of the wing, the so-called winglet.

The pelvic girdle of the skeleton is formed by thin iliac, pubic and ischial bones that grow together in adult birds into a single bone. The posterior ends of the pubic and ischial bones in most birds (except for some ostriches) do not converge, so the pelvis remains open from below.

The skeleton of each of the hind limbs consists of a large bone of the thigh, two bones of the lower leg (tibia and fibula), the tarsus and phalanges of the fingers. The tibia is strongly reduced and accreted to the tibia. In the process of ontogenesis, the bones of the main row of the tarsus grow to the lower end of the tibia. The remaining bones of the tarsus and three bones of the metatarsus merge into a single elongated bone - the tarsus. The phalanges of the fingers are attached to the lower end of the tarsus.

Musculature. The pectoral and subclavian muscles, which set the wings in motion, are especially developed. The muscles of the legs are also powerful, doing a lot of work when walking a bird and moving along tree branches, during takeoff and landing.

The nervous system, especially the central part, in birds has a more complex structure than in reptiles, which corresponds to a higher level of vital activity. The bird's brain is distinguished by the large size of the forebrain hemispheres, the strong development of the optic hillocks of the midbrain and a huge corrugated cerebellum (Fig. 252). The roof of the hemispheres has a smooth surface, and the gray medulla in it is weakly expressed. The strong development of the visual hillocks of the midbrain, which carry the visual function, is due to the importance of vision in the life of birds. The cerebellum is large and complex in structure. Its middle part - the worm - almost touches the hemispheres with its front edge, and covers the medulla oblongata with its posterior end. The worm is covered with characteristic transverse grooves. The development of the cerebellum is associated with flight, which requires precisely coordinated movements. There are 12 pairs of cephalic nerves in birds.

Digestive organs begin with the oral cavity. Teeth in modern birds are absent - they are partially replaced by the sharp edges of the horny cover of the beak, with which the bird captures, holds and sometimes grinds food (Fig. 253). The long esophagus in many birds expands into a crop; here the beggar, being treated with saliva, swells and softens. From the esophagus "food enters the glandular stomach, where it mixes with digestive juices. From the glandular stomach, food passes into the muscular stomach. Its walls are folded by powerful muscles, and in a cavity lined with a hard shell, there are usually small stones swallowed by a bird. These stones and folds the walls of the stomach during the contraction of the muscles of the walls grind food.

The intestines of birds are relatively short. It distinguishes between a longer thin and less extended thick sections. At the border of these sections, two blind outgrowths depart from the intestine. The rectum is not developed, so the feces do not accumulate in the intestines, which makes the weight of the bird lighter. The intestine ends with an expansion - a cloaca, into which the ureters and ducts of the genital glands open. Secrets of the large two-lobed liver and pancreas, entering the duodenum, facilitate the digestion of food.

The expenditure of a huge amount of energy by birds during flight and high level metabolism necessitate the absorption of large masses of food. So, a small bird of our forests, a king, per day consumes an amount of food exceeding "/ 4 body weight. Digestion processes in birds proceed very quickly: in waxwings, rowan berries pass the entire intestine in 8-10 minutes, and in a duck opened 30 minutes after after she swallowed a 6 cm long crucian carp, it was no longer possible to find its remnants in the intestines.

Rice. 253. Internal structure of a bird (pigeon):

/ - opened pigeon; // - section of the stomach of a pigeon;

/ - trachea; 2 - the esophagus; 3 - goiter; 4 - lung; 5 - air bags;

6 - a heart; 7 - glandular stomach; 8 - gizzard

The respiratory organs of birds also bear signs of adaptation to flight, during which the body needs increased gas exchange (Fig. 254). A long trachea departs from the bird's pharynx, which is divided into two bronchi in the chest cavity. At the site of the division of the trachea into bronchi, there is an expansion - the lower larynx, in which the vocal cords are located; its walls have bony rings. The lower larynx plays the role of a vocal apparatus and is especially strongly developed in birds that sing or make loud sounds.

The lungs of birds have a spongy structure. The bronchi, entering the lungs, disintegrate into smaller and smaller branches. The latter end in the thinnest blind tubules - bronchioles, in the walls of which the capillaries of blood vessels pass.

Part of the branching of the bronchi extends beyond the lungs, continuing into thin-walled air sacs located between the muscles, among the internal organs and in the cavities of the tubular bones of the wings. These bags play a large role in the breathing of the bird during flight. In a sitting bird, breathing is carried out by expanding and contracting the chest. In flight, when the moving wings need solid support, the chest remains almost motionless and the passage of air through the lungs is mainly due to the expansion and contraction of the air sacs. This process is called double breathing, since the release of oxygen into the blood occurs both during inhalation and exhalation. The faster the flapping flight, the more intense the breathing. When the wings are lifted, they stretch and air is sucked into the lungs and further into the bags. When the wings are lowered, exhalation occurs, and air passes through the lungs silt bags, which promotes the oxidation of blood in the lungs.

/ trachea;
2-- lungs; 3-11
- air bags

Rice. 255. The circulatory system of a bird (pigeon):

/ spicy atrium; 2 - right ventricle of the heart; 3 - left pulmonary artery; 4 right pulmonary artery; 5 - left atrium; 6 - the left ventricle of the heart; 7 - the right aortic arch; H, 9 - unnamed arteries; 10 -12 - carotid arteries; 13 - subclavian artery; 14-- left thoracic artery; 15 - aorta; 16 - the right femoral artery; 17 renal artery; 18 -the sciatic artery; 19 -- iodine artery; 20 posterior mesenteric artery;
21 - tail artery; 22 tail vein; 23 - portal vein of the kidneys; 24 - femoral vein; 25 - iodine-I! tire yen; 2 in posterior vena cava; 27 - intestinal vein; 28
- supra-intestinal vein; 29 renal vein; 30 - jugular vein; 31
- subclavian vein; 32 - anterior vena cava

The circulatory system of birds has two circles of blood circulation (Fig. 255). A large heart is completely divided into right and left halves and has left and right atria and left and right ventricles. This achieved complete separation of arterial and venous blood flows. Arterial blood, coming from the lungs to the pulmonary vein, enters the left atrium, and from there - into the left ventricle, from which it goes into the aorta. Venous blood from all over the body enters the right atrium, and from it to the right ventricle, in order to then go through the pulmonary artery to the lungs.

In embryos of birds, like reptiles, both the left and right aortic arches are laid, but in the process of embryonic development of the animal, the left atrophies. Starting from the left ventricle of the heart, the right aortic arch bends to the right (which is why it is called right), turns back and continues with the trunk of the aorta, stretching under the spine. Large paired unnamed arteries depart from the aortic arch, which soon divide into the carotid arteries that carry blood to the head, and the powerful thoracic and subclavian arteries that go to the pectoral muscles and wings. From the dorsal aorta, arteries branch off to various parts of the bird's trunk and to the legs. The venous system of birds is basically similar to that of reptiles.

The high activity of the metabolic process in birds makes it necessary to quickly and abundantly deliver nutrients and oxygen to all parts of the body. Therefore, their blood circulation occurs very quickly, which is ensured by the energetic work of the heart. So, in many small birds, the heart beats more than 1,000 times per minute (in humans, 60-80 times).

The excretory organs of birds are also adapted to the intensive metabolism in the body, as a result of which the volume of decay products to be removed increases. The kidneys in birds are large and lie in the depressions of the pelvic bones. From them, the ureters depart, opening into the cloaca. Thick urine enters the cloaca, from where it is excreted along with the feces.

Reproductive organs. The two testes lying in the abdominal cavity are bean-shaped. The vas deferens depart from them, opening into the cloaca. In some birds (geese), males have a copulatory organ. Females usually have only one, left, ovary lying near the kidney. The egg released from the ovary enters the unpaired oviduct, in the upper part of which fertilization takes place. After passing through the oviduct, the egg acquires a protein shell, and once in a wider uterus, it becomes covered with a calcareous shell. Through the final section of the female's genital tract - the vagina - the egg enters the cloaca, and from there it is taken out.

Rice. 256. The structure of a bird's egg:

/ ...... shell; 2 -..... nodoshell shell; ,4 -

air chamber; * "/ protein; L vitelline membrane; in yolk; 7 - embryonic disc;
H ~ white yolk; 9 -yellow yolk; 10 --chalazi

The bird's egg has (relative to the size of the animal) very large sizes, as it contains many nutrients in the form of yolk and protein (Fig. 256). The embryo develops from a small embryonic disc located on the surface of the yolk.

At the blunt end of the egg, the shell and shell membrane contains a cavity filled with air; it helps the fetus to breathe. The development of a chick in an egg is shown in Fig. 257.

Rice. 257. Development of a bird embryo:

/- IV - successive stages of development of chmbryo; / - embryo; 2 - yolk; 3 -protein; 4-- amshutic fold; 5 cervical cavity; 6 "- air chamber; 7 - ~ shell; H-
serosa; 10 - amnion cavity; // - allantois; 12 ■- yolk sac

Bird ecology. The main form of movement of most birds is flight. Adaptation to flight caused a number of the described changes in the structure of the organism of these animals, and also left an imprint on all types of their vital activity. Due to the ability to fly, birds have enormous opportunities for distant migrations and dispersal: it was flight that allowed them to populate all oceanic islands, often lying hundreds of kilometers from the mainland. Flying helps the birds avoid enemies. During the flight, many birds search for food or look out for it on the ground.

The nature of the flight different types birds are far from the same - it is always in accordance with their way of life. There are two main types of bird flight: soaring and rowing. Soaring is the flight of birds on more or less motionless, outstretched wings. This flight can be carried out with a gradual decrease in the bird in the air. But often a bird, by soaring, can maintain its gained height above the ground or even rise up (achieved through the use of updrafts by the bird). Rowing flight is carried out by flapping the wings. In many birds, this active form of flight alternates with soaring in the air. During a calm rowing flight, a crow makes an average of 2.9, and a seagull - 2.2 wings per second. The maximum possible flight speed of a swallow is 28 m, a wood grouse is 16 and a swan is 14 m per second. Some birds can fly more than 3 thousand km without stopping for rest.

The ability for active flight, warm-bloodedness and a high level of development of the central nervous system provided birds with the possibility of wide distribution on Earth. With the adaptation of birds in the course of evolution to life in different conditions (forests, open spaces, water bodies), the formation of different ecological groups, differing in appearance and specific structural features, is associated.

Tree birds - inhabitants of various forests and shrubs. This group includes woodpeckers, parrots, nuthatches, pikas, cuckoos, starlings, blackbirds, pigeons, wood grouses, hazel grouses, etc. They forage and usually nest in trees, less often on the ground. The most specialized birds adapted to tree climbing (parrots, woodpeckers, nuthatches) have strong legs armed with curved claws. Woodpeckers have two fingers directed forward, two - back, which allows them to deftly climb tree trunks, leaning on the hard and elastic tail feathers. When moving along the branches of trees, parrots use not only their hind limbs, but also their beak.

Land birds - inhabitants of open spaces - meadows, steppes and deserts. This group includes ostriches, bustards, little bustards, some waders. They feed and nest on the ground. In search of food, they move mainly by walking and running, rather than flying. They are large and medium-sized birds with a massive and wide body and a long neck. The legs are long and strong, with short and thick toes, the number of which can be reduced to three, and in the African ostrich, to two.

Wading birds inhabited by swampy meadows, swamps, thickets of coastal reservoirs. Typical representatives: herons, storks, cranes, many waders. The feed is usually collected on the ground. Nests are made on the ground or in trees. These are large or medium-sized birds. Most have long, thin legs with elongated toes, with the help of which they can easily move on sticky ground or shallow water. The head is small, with a long, hard beak. The wings are well developed. The tail is short. The plumage is loose, with poorly developed down.

Waterfowl a significant part of their life is spent on reservoirs. This group includes loons, grebes, guillemots, guillemots, penguins, cormorants, pelicans, ducks, geese, swans. They swim well, and many dive, but they walk on land and usually fly badly, and some do not fly at all (penguins). Many birds forage (fish, molluscs, crustaceans) in water, others feed on land with vegetative parts of plants and seeds. They nest on the banks of water bodies, on the ground, in trees, in reed thickets, on rocks and in their crevices, in burrows. These are large and medium-sized birds with a body somewhat flattened from the ventral side and a short tail. The legs are set far back, which provides an almost vertical position of the body when walking. They have dense plumage with well-developed down, swimming membranes on their paws, and most have a developed coccygeal gland.

Air-water birds unlike the previous group, they are less associated with water bodies. The group includes gulls, terns, petrels. They usually fly well, swim well, but dive poorly. Soaring flight using air swirls over the waves or different air speeds. They feed mainly on fish, which they look out for during the flight, then quickly rush at it and pull it out of the water with their strong and long beak, bent at the end. They often nest on the banks of rivers, lakes, seas, on rocky ledges of sea shores. These are large and medium-sized birds with an elongated body, long, sharp wings and short legs, on which the three front toes are connected by a swimming membrane. The plumage is dense, with a lot of down.

Airborne birds a significant part of the daylight hours is spent in the air, where they catch insects with their short, wide-opening beak. Typical representatives: swifts, swallows, nightjars. They are excellent flyers with fast and maneuverable flight. They usually nest in buildings, in burrows but on river banks, on the ground. Their body is elongated, the neck is short, the wings are long and narrow. The legs are short, making it difficult to walk on the ground.

Bird feeding. Most birds are carnivorous, others are herbivorous or omnivorous. There are species that feed mainly on vegetative parts of plants (geese), berries (blackbirds, waxwings), seeds (sparrows, crossbills), nectar (hummingbirds), insects (cuckoos, woodpeckers, many passerines), fish (gulls, cormorants, pelicans), frogs (ducks, storks, herons), lizards and snakes (storks, some diurnal predators), birds (hawks), rodents (owls, many diurnal predators). Some predators prefer to eat carrion (vultures, vultures, vultures). The nature of food can vary depending on age: most granivorous birds feed their chicks with insects. The composition of poverty also varies according to the seasons of the year. For example, the black grouse in summer feeds on green parts of plants, berries and insects, and in winter - mainly on pine needles, buds, shoots and catkins of birch and alder.

Annual periodicity in the life of birds. In birds, as in other animals, the annual frequency of life is closely related to seasonal changes in living conditions and is of great adaptive value. It allows you to time the most crucial moment in the life of each species - reproduction - to a certain season, when conditions for feeding the chicks will be most favorable. The following stages of the annual cycle of birds can be distinguished: preparation for breeding, reproduction, molting, preparation for winter, wintering.

Preparing for breeding expressed in the formation of pairs. Association at mating time in bunks (monogamy) is characteristic of most bird species. However, the duration of existence of pairs in different birds is significantly different. Swans, storks, eagles form pairs for several years or perhaps even for life. Other birds mate during the breeding season, and many ducks only mate until lay. In a smaller number of bird species, pairs are not formed and the male fertilizes several females during the breeding period, which bear all the care of the offspring. This phenomenon has received the name and about ln-gamia (polygamy). It is characteristic of black grouse, pheasants, wood grouse, domestic chickens. Sexual dimorphism is especially pronounced in these birds.

Breeding into pairs in birds is accompanied by mowing: birds take different poses, keep their plumage unusually, emit special sounds, and in some polygamous species there are fights between males. The mating behavior of birds facilitates the meeting of individuals of different sexes and the formation of pairs, stimulates the synchronous maturation of the reproductive products of both partners.

The fertility of birds is much less than that of reptiles, which is associated with the presence of various forms of care for the offspring in birds (nesting, incubation and feeding of chicks). The number of eggs in a clutch ranges from 1 (penguins, guillemots) to 22 (gray partridge). Most birds incubate their clutch. In polygamous species, incubation is carried out only by the female (chickens, anseriformes), in monogamous species - alternately by a male and a female (pigeons, gulls, many passerines) or only by a female, and the male feeds her and protects the nesting area (owls, diurnal predators, some passerines).

The duration of incubation in different birds is different and depends on the size of the egg and bird, the type of nest and the intensity of incubation. Small passerines incubate for 11-12 days, crow - 17, swans - 35-40. The duration of incubation in poultry: in a chicken 21 - days, in a duck - 28, in a goose - 30, in a turkey - 28, 29 days.

Depending on the degree of development of the chicks that have just hatched from the eggs, birds are divided into brood, semi-brood, and chicks (Fig. 258). The chicks of brood birds are pubescent, sighted, capable of feeding on their own after a short time (chickens, anseriformes, ostriches). Chicks of semi-brood birds hatch sighted and pubescent, but are fed by their parents until they acquire the ability to fly (gulls, guillemots, petrels). In chick birds, chicks are naked, blind, and remain in the nest for a long time (passerines, woodpeckers, pigeons), where their parents feed them intensively. So, a pair of flycatchers, tits or warblers brings food to their chicks up to 450-500 times a day.

After the end of feeding the chicks, the colony usually breaks up and the birds unite in flocks. The highest mortality is observed in the first year of bird life. Sometimes it can reach more than 50 % the number of individuals flew out of the nest. Birds reach sexual maturity in different ages... Most small and medium-sized birds (many passerines) begin to breed as early as the next year of life, larger birds (hooded crow, ducks, small carnivores and gulls) - by the 2nd year, and loons, eagles, petrels - by 3-4 -m, ostriches - on the 4th - 5th year.

Rice. 258. Chicks of different birds at the same age:

/ - chicks (skate); // - semi-brood (eagle); /// - brood (partridge)

The average life span of small passerine birds is 1–1.5 years, and the maximum life span is 8–10 years. Larger bird species can live for 40 years or more.

Molting proceeds differently in different birds. In some species (passerines) it is gradual, in others (chickens, anseriformes) it is stormy. Linear anseriformes lose their ability to fly for 2-5 weeks. Molting usually begins immediately after breeding. In males of many bird species that are not involved in breeding, molt occurs earlier than in females. Shedding males of wood grouses and black grouses keep one by one in remote areas of the forest, and duck drakes accumulate in large numbers during the molt period in hard-to-reach wetlands.

Preparing for winter . During this period, birds begin to wander in search of food. Intense nourishment ensures fat accumulation. Some birds tend to store food, which makes their wintering easier. Jays collect acorns and bury them in the soil or under the forest floor, and nutcrackers - nuts. In winter, birds use these reserves only partially. Another part of the seeds is eaten by murine rodents and insects or, remaining until spring, germinates. Nuthatches and tits hide the seeds of various trees in the cracks in the bark, providing themselves with 50-60% fodder. Small owls (passerine and uplifted owls) harvest the carcasses of mouse-like rodents for the winter and put them in the hollows of trees. Birds find their pantries, apparently, thanks to memory and sense of smell.

Wintering but. During the winter period, birds face great difficulties in obtaining the right amount of feed. In search of habitats that can most fully provide this or that species with food and protective conditions, many birds begin to make directional movements (migrations and migrations). Only sedentary birds remain in the places where their breeding took place, and if they change their habitats, they fly away no further than several tens of kilometers (wood grouses, hazel grouses, woodpeckers, sparrows, tits). Birds can fly away hundreds of kilometers, but they usually stay within the same natural zone (waxwings, tap dancers, bullfinches). The farthest migrations are made by migratory birds wintering in other natural zones located thousands of kilometers from nesting sites.

The division of birds into sedentary, nomadic and migratory birds is complicated by the fact that the same species can behave differently in different parts of its range. So, the hooded crow in the south of the European part of the USSR is a sedentary species, in the south it is migratory. Changes in weather and feeding conditions over the years also affect the nature of the mobility of birds. In warm winters, with sufficient food supply, some species migrating for a given area remain to winter in their breeding sites (ducks, rooks, blackbirds). This indicates that the main reason for bird migration is seasonal changes in living conditions. In areas where these changes are more pronounced in seasons, the number of migratory species is greater. So, in the USSR, out of 750 bird species, 600 are migratory, wintering mainly in the British Isles, Southern Europe, the Mediterranean, Africa and Asia.

The migratory paths of birds are enormous. The flight path of our warblers and swallows wintering in Africa is 9-K) thousand km, and the polar tern from the coasts of the Barents Sea to the coasts of Africa is 16-18 thousand km. The flyways of waterfowl and wading birds are confined to river valleys and sea coasts, where there are conditions suitable for their rest and feeding. Many birds fly in a wide front. Small passerines cover a distance of 50 ..... 100 km per day, ducks - 100-

500, storks - ~ 250, woodcocks 500 km. Birds usually spend 1-2 hours per day for flight, using the rest of the time for stops for rest and feeding. Crossing bodies of water, they fly thousands of kilometers without rest. In spring, bird stops are more rare and short-lived than in autumn; therefore, spring migrations usually occur at a faster rate than autumn ones.

Bird migration is one of the most interesting and poorly studied questions of bird biology. Until now, the mechanism that determines the orientation of birds during migration has not been fully understood. On the basis of observations in nature and the setting of experiments, it was possible to reveal that migratory birds can orient themselves in the position of the sun, moon, stars, and in the features of the landscape. The innate migratory instinct plays an important role in the migratory behavior of birds and the choice of a general direction during flight. However, it manifests itself in the presence of a certain amount of environmental factors. Under the influence of environmental conditions, it is possible to change this innate instinct.

Bird migration has developed over millennia. The influence of the Ice Age on the formation of bird migration routes in the Northern Hemisphere is indisputable. The modern flyways of some birds repeat the historical path of their dispersal in the postglacial period.

The method of ringing is of great importance for the study of bird migration, when chicks, before leaving the nest or adult birds, are put on a metal ring on their paws with the number and designation of the institution conducting the tagging. In our country, all information about ringing and the extraction of ringed birds is sent to the Banding Center of the USSR Academy of Sciences (Moscow). Annually about 1 million birds ring around the world, of which more than 100 thousand in the USSR. Ringing allows you to trace migration routes, flight speed, lifespan and other important issues of bird ecology.

The economic value of birds. The role of birds in human economic activity is great and diverse. Birds domesticated by humans (chickens, geese, ducks, turkeys, guinea fowls, pigeons) have long been used to obtain meat, eggs, down, feathers and other valuable products and industrial raw materials from them. In our country, poultry farming is the most important and rapidly developing branch of animal husbandry. Many species of wild birds (chickens, anseriformes, some waders) serve as objects of sports and commercial hunting, which makes it possible to additionally involve a significant amount of tasty meat in the economic circulation.

The role of birds in the extermination of insects and mouse-like rodents - agricultural pests is great. The importance of tits, flycatchers, nuthatches, starlings, thrushes and many other birds as regulators of the number of harmful insects especially increases during the period of feeding the chicks. Thus, the family of the common starling during the nesting period destroys 8-10 thousand May beetles and their larvae, or over 15 thousand caterpillars of the winter moth. Many birds of prey, owls, gulls, storks and a number of others exterminate mice, voles, ground squirrels, rats, hamsters and other harmful rodents. The usefulness of birds is associated with their ability to quickly find and concentrate in the centers of mass reproduction of pests, and for many species of birds - to switch to numerous, although often not typical for them, food. So, in the years of mass reproduction of murine rodents, rooks, gulls, etc. begin to feed on them.

Some birds act as plant distributors. For example, in the taiga of Eastern Siberia, the restoration of cedar is often associated with the activity of nutcracker. Jays are involved in the settlement of oak. Waxwing, blackbirds, hazel grouses and many others carry seeds of mountain ash, bird cherry, blackthorn, elderberry, viburnum, euonymus, blueberry, raspberry, lingonberry, etc.

Rice. 259. Various types of crowbars for hezdonapiya beneficial insectivorous BIRDS

To increase the number and attract useful birds, they create favorable conditions for their nesting, hang artificial nests: birdhouses, nest boxes (Fig. 259),

carry out winter feeding it. e. When artificial nesting sites are hung, the number of duylogynpkov (flycatchers, titmice, starlings) sharply increases.

In some cases, birds can cause some damage. Rooks, useful in killing soil insects, sometimes harm crops (especially corn) by pecking seeds and pulling out seedlings. Wandering starlings peck at ripe cherries and grapes. In the southern regions of our country, in some places, sparrows cause serious damage to the grain harvest. Bee-eater, which exterminates bees, can be harmful to beekeeping. Reed Harrier and Hooded Crow harm the hunting economy in some places. In a collision with high-speed aircraft in the air, birds sometimes cause serious accidents, which leads to the creation of a system for scaring birds from the territory of airfields. It is also necessary to take into account the role of birds in the spread of some diseases dangerous for humans and farm animals (psittacosis, influenza, encephalitis, etc.).

Birds - highly organized warm-blooded animals adapted to flight. Due to their large numbers and wide distribution on Earth, they play an extremely important and diverse role in nature and human economic activity. More than 9 thousand modern bird species are known.

General features of the organization of birds in connection with their adaptation laziness to flight:

Rice. 45. Topography of body parts of birds: 1 - forehead; 2 - bridle; 3 - crown; 4 - ear coverts; 5 - neck; 6 - back; 7 - upper tail; 8 - upper tail coverts; 9 - steering feathers; 10 - lower tail coverts; 11 - undertail; 12 - shin; 13 - back finger; 14 - tarsus; 15 - sides; 16 - belly; 17 - goiter; 18 - throat; 19 - chin; 20 - cheeks; 21 - mandible; 22 - beak; 23 - shoulder feathers; 24 - upper wing coverts; 25 - secondary flywheels; 26 - primary flywheels.

Respiratory system - lungs. A flying bird has breath doublenoe: gas exchange in the lungs is carried out both during inhalation and exhalation, when atmospheric air from air bags enters the lungs. Due to double breathing, the bird does not suffocate during flight.

A heart four-chamber, all organs and tissues are supplied with pure arterial blood. As a result of the intensive process of life, a lot of heat is generated, which is retained by the feather cover. Therefore, all birds - warm-blooded animals with a constant body temperature.

The excretory organs and types of end products of nitrogen metabolism are the same as in reptiles. Only the bladder is missing due to the need to lighten the bird's body weight.

Like all vertebrates, the bird's brain has five sections. Most developed cerebral hemispheres of the forebrainha, covered with smooth bark, and cerebellum, thanks to which the birds have good coordination of movements and complex forms of behavior. The orientation of birds in space is carried out with the help of keen vision and hearing.

Birds are dioecious, most species are sexually dimorphic. In females, only left ovary. Fertilization is internal, development is direct. Birds of most species lay eggs in the nests, warm them with the heat of their body (incubation), feed the hatched chicks. Depending on the degree of development of the chicks hatched from the eggs, nesting and brood birds.

Features of the structure and life

In birds, the head is small, the neck is long and extremely mobile. The jaws are devoid of teeth, elongated and form a beak, covered with a horny sheath. The shape of the beak varies greatly due to the variety of food items. Large eyes are located on the sides of the head, and below them there are external auditory openings.

The forelimbs are transformed into a flying organ - wings. The hind limbs have a varied structure, which depends on the living conditions and methods of obtaining food. The lower legs and toes are covered with horny scales. The tail is short, equipped with a fan of tail feathers, and different birds have an unequal structure.

Leather birds are thin, dry, devoid of glands. The only exception is the coccygeal gland, located under the root of the tail. It secretes a fat-containing secretion with which the bird lubricates the feathers with the help of its beak. The gland is highly developed in waterfowl. Their skin is covered with a kind of horny covering, consisting of feathers. Bird feathers serve the purposes of thermoregulation, mainly heat retention, create a "streamlined" body surface and protect the skin from damage. Although the body of birds is usually completely covered with feathers (with the exception of some bare areas - around the eyes, at the base of the beak, etc.), feathers do not grow on the entire surface of the bird's body. In flying birds, feathers are noted only on certain areas of the skin (areas of the body that bear feathers - pterilia, without feathers - apteria), and in flightless birds they evenly cover the entire body.

Rice. 46. ​​Apteria and pterilias on the body of a bird. Dots mark pterilia

but

Rice. 47. The structure of the flight feather: a - general view; b - a diagram of the structure of the fan; 1 - ochin; 2 - rod; 3 - fan; 4 - barbs of the first order; 5 - barbs of the second order; 6 - hooks.

The vast majority of birds have contour and down feathers. A contour feather consists of a core, a point and a fan (fig. 47). The fan is formed by numerous plates extending from the rod on both sides - first-order barbs, on which thinner barbs of the second order are interlocked with hooks. As a result, the interlocked fan is a light elastic plate, which can be easily restored in the event of a rupture (for example, by the wind). Contour feathers form the flying planes of the wings, tail, and also give the bird a streamlined surface. Down feathers have a thin shaft and are devoid of second-order barbs, due to which they do not have solid fans. Down feathers are located under the contour feathers. Their main function is to keep the body warm of the bird.

Skeleton birds (Fig. 48) is durable and light. Strength is provided by early fusion of a number of bones, lightness - by the presence of air cavities in them.

Structure skulls birds are similar to the structure of the skull of reptiles, but differs in great lightness, a voluminous cerebral box, which ends with a beak, and carries huge eye sockets from the sides.

Rice. 48. Bird skeleton: 1 - lower jaw; 2 - skull; 3 - cervical vertebrae; 4 - thoracic vertebrae; 5 - humerus; 6 - bones of the metacarpus and fingers; 7 - forearm bones; 8 - scapula; 9 - ribs; 10 - pelvis; 11 - caudal vertebrae; 12 - coccygeal bone; 13 - femur; 14 - shin bones; 15 - tarsus; 16 - phalanges of the fingers; 17 - keel of the sternum; 18 - sternum; 19 - coracoid; 20 - collarbone.

In an adult bird, the bones of the cranium grow together until the sutures disappear completely.

Spine, like all terrestrial vertebrates, it consists of five sections - cervical, thoracic, lumbar, sacral and caudal. Only the cervical region retains great mobility. The thoracic vertebrae are inactive, and the lumbar and sacral vertebrae firmly grow together with each other (complex sacrum) and with the bones of the pelvis. Some bones of the shoulder girdle also grow together: the saber-shaped scapula with the crow's bone, the clavicle with each other, which ensures the strength of the shoulder girdle, to which the front limbs - the wings - are attached. They contain all the typical sections: the humerus, ulna and radius of the forearm and the hand, the bones of which grow together. Of the fingers, only three are preserved.

The pelvic girdle provides reliable support for the hind limbs, which is achieved by the fusion of the ilium along its entire length with the complex sacrum. Due to the fact that the pelvic (pubic) bones do not grow together and are widely spaced, the bird can lay large eggs.

The powerful hind limbs are formed by bones typical of all terrestrial animals. To strengthen the tibia, the tibia is added to the tibia. The bones of the metatarsus grow together with part of the bones of the tarsus to form a bone characteristic only of birds - tarsus. Of the four fingers, most often three are directed forward, one is directed backward.

The ribcage is formed by the thoracic vertebrae, ribs and sternum. Each rib consists of two bony sections - dorsal and abdominal, movably articulated with each other, which ensures the approach or abduction of the sternum from the spine during breathing. The sternum in birds is large and has a large protrusion - the keel, to which the pectoral muscles are attached, which set the wings in motion.

Due to the great mobility and variety of movements musklatura birds are highly differentiated. The pectoral muscles (1/5 of the total mass of the bird), which are attached to the keel of the sternum and serve to lower the wings, reached the greatest development. The subclavian muscles located under the pectoralis provide wing lift. The flight speed of birds is different: 60-70 km / h for ducks and

65-100 km / h for a peregrine falcon. The highest speed was recorded for the black swift - 110-150 km / h.

The powerful musculature of the legs of birds that have lost the ability to fly allows them to move quickly over land (ostriches run at an average speed of 30 km / h).

Intense physical activity of birds requires a lot of energy.

Due to this digestive systemnew has a number of features. Food is captured and held by the horny beak, moistened with saliva in the oral cavity and moved into the esophagus. At the base of the neck, the esophagus expands into a goiter, which is especially well developed in granivorous birds. In the goiter, food accumulates, swells and partially undergoes chemical processing. In the front, glandular part of the stomach of birds, chemical processing of incoming food takes place, in the back, muscular, its mechanical processing. The walls of the muscular section work like millstones and grind hard and coarse food. Pebbles swallowed by birds also contribute to this. From the stomach, food sequentially enters the duodenum, small and short colon, which ends in a cloaca. Due to the underdevelopment of the rectum, birds often empty the intestines, which makes them lighter. Powerful digestive glands (liver and pancreas) actively secrete digestive enzymes into the duodenal cavity and process food, depending on its type, in 1 - 4 hours. Large energy expenditures require a significant amount of feed: 50 - 80% of the body weight per day in small birds and 20 - 40% in large birds.

In connection with the flight, the birds have a peculiar structure. organew breath. The lungs of birds are dense, spongy bodies. The bronchi, entering the lungs, branch strongly into them to the thinnest, blindly closed bronchioles, entangled in a network of capillaries, where gas exchange takes place. Part of the large bronchi, without branching, goes beyond the lungs and expands into huge thin-walled air sacs, the volume of which is many times greater than the volume of the lungs (Fig. 49).

Air sacs are located between various internal organs, and their branches run between muscles, under the skin and in the bone cavity. The act of breathing in a flightless bird is carried out by changing the volume of the chest due to the approach or removal of the sternum from the spine. In flight, such a breathing mechanism is impossible due to the work of the pectoral muscles, and it occurs with the participation of air sacs. When the wings are raised, the bags are stretched and air through the nostrils is forcefully sucked into the lungs and further into the bags themselves. When the wings are lowered, the air sacs are compressed and the air from them enters the lungs, where gas exchange occurs again. The exchange of gases in the lungs during inhalation and exhalation is called double breathing. Its adaptive meaning is obvious: the more often the bird flaps its wings, the more actively it breathes. In addition, air bags keep the bird from overheating during fast flight.

Rice. 49. Respiratory system of a pigeon: 1 - trachea; 2 - lung;

3 - air bags.

The high level of bird life is due to a more perfect circulatory system in comparison with the animals of the previous classes, they had a complete separation of the arterial and venous blood flows. This is due to the fact that the heart of birds is four-chambered and is completely divided into the left - arterial, and right - venous, parts. There is only one aortic arch (right) and departs from the left ventricle. Pure arterial blood flows in it, supplying all tissues and organs of the body.

Rice. 50. Internal organs of birds: 1 - esophagus; 2 - glandular stomach; 3 - spleen; 4 - gizzard; 5 - pancreas; 6 - duodenum; 7 - small intestine; 8 - rectum; 9 - cecum; 10 - cloaca; 11 - goiter; 12 - liver; 13 - trachea; 14 - lower larynx; 15 - light and air bags; 16 - testes; 17 - vas deferens; 18 - kidneys; 19 - ureters.

A pulmonary artery departs from the right ventricle, carrying venous blood into the lungs. Blood quickly moves through the vessels, gas exchange is intense, and a lot of heat is released. The body temperature is kept constant and high (in different birds from 38 to 43.5 ° C). This leads to a general rise in the vital processes of the bird's organism.

In response to a decrease in the temperature of the external environment, birds do not hibernate, like amphibians and reptiles, but intensify their movement - migrations or flights, that is, they migrate to more favorable conditions of existence.

Highlighting the end products of metabolism are carried out by the large pelvic kidneys. The bladder is missing. Like most reptiles, the product of nitrogen metabolism is uric acid. In the cloaca, the water contained in the urine is absorbed and returned to the body, and thick urine is mixed with the remnants of undigested food and excreted.

Brain birds differ from the brain of reptiles in the large size of the hemispheres of the forebrain and cerebellum. Birds have a sharp vision and excellent hearing. Their eyes are large, especially in night and twilight birds. The accommodation of vision is double, which is achieved by changing the curvature of the lens and the distance between the lens and the retina. All birds have color vision. The organ of hearing is represented by the inner, middle ear and external auditory canal. The sense of smell is poorly developed, with the exception of a few species.

Reproduction birds are characterized by a number of progressive features: 1) fertilized eggs, covered with a strong shell, are deposited not just in the external environment, but in special structures - nests; 2) eggs develop under the influence of parental body heat and do not depend on accidental weather, which is typical for developing eggs of fish, amphibians and reptiles; 3) nests are protected from enemies by their parents; 4) chicks are not left to fend for themselves, but for a long time they are fed, protected and trained by their parents, which contributes to the preservation of young animals.

Fertilization in birds is internal. Due to the laying of large eggs, which weigh down the birds, only the left ovary is developed in females. Birds have the largest eggs in the animal kingdom due to the large amount of yolk they contain. The glands of the oviduct secrete subshell and shell membranes, through the numerous pores of which the embryo's gas exchange with the external environment takes place.

The origin of birds. Birds are related to reptiles. Probably, the separation of birds from the group of reptiles, which were the ancestors of crocodiles, dinosaurs and flying dinosaurs, occurred at the end of the Triassic or early Jurassic period of the Mesozoic era (i.e. 170 - 190 million years ago). The evolution of this group of reptiles proceeded by adapting to climbing trees, in connection with which the hind limbs served to support the body, and the front ones were specialized for grasping branches with the fingers. Subsequently, the ability to flutter from branch to branch and glide flight developed.

The immediate ancestors of the birds have not been found. Known paleontological finds of an intermediate link between reptiles and birds - archeopteryx.

Nesting, migrations and flights. Seasonal phenomena in the life of birds they are more pronounced than in other classes, and have a completely different character.

With the onset of spring, birds begin to reproduce, they break up into pairs, mating games (mating) take place, the nature of which is specific for each species. Many species form pairs for life (large predators, owls, herons, storks, etc.), others are seasonal pairs. There are species of birds that do not form pairs at all, and all care for the offspring falls to only one sex - the female.

Bird nests are varied, but each species has a more or less definite shape: hollow, burrow, molded and spherical nests, etc. Some species of birds do not build nests (guillemot, nightjar).

The number of eggs in a clutch varies in different bird species from 1 (guillemots, gulls, diurnal predators, penguins, etc.) to 26 (gray partridge). In some birds, incubation of eggs is carried out by one of the parents (only by females - in hens, passerines, anseriformes, owls, or only males - in Australian and American ostriches), in other birds - by both. The duration of incubation is different and is to some extent related to the size of the egg - from 14 days in passerines to 42 in the African ostrich.

Depending on the degree of development of chicks when hatching from an egg, two groups of birds are distinguished: brood and nesting(chicks). In the first, chicks appear sighted, covered with fluff, able to walk and peck food on their own (ostriches, chickens, anseriformes). In nesting nestlings, they are completely or partially naked, blind, helpless, remain in the nest for a long time and are fed by their parents (passerines, woodpeckers, swifts, etc.).

In summer, birds molt, grow, store nutrients. With the onset of autumn cold weather, they do not reduce the level of their vital activity, like amphibians and reptiles, but, on the contrary, increase it, increasing their mobility and wandering in search of food. In addition, birds become very fat and thus adapt to wintering.

Sedentary birds(ptarmigan, tits, sparrows, jays, crows, etc.) keep in the same area with the onset of unfavorable conditions. Nomadic birds(waxwings, bullfinches, crossbills, tap dancers, etc.) leave their summer habitats and fly away at relatively short distances. Migration birds (storks, geese, sandpipers, swifts, orioles, nightingales, swallows, cuckoos, etc.) leave their nesting areas and fly away to wintering grounds for many thousands of kilometers. Most of them fly in flocks, and only a few (cuckoo) fly alone. Large birds fly in a certain formation (geese - in a line, cranes - in a wedge), small birds - in chaotic flocks. The insectivores are the first to fly away, then the granivores and later than all the waterfowl and wading birds.

It is believed that bird migration arose as a result of periodic changes in climatic conditions associated with the changing seasons. The immediate causes of flights are considered to be complex interactions, both external (shortening daylight hours, lowering temperatures, worsening conditions for obtaining food) and internal factors (physiological changes in the body due to the end of the breeding period).

In the study of flights, the ringing method is of great importance. The caught birds are put on an aluminum ring on their paws, on which their number and the institution conducting the ringing are indicated. In the USSR, ringing has been carried out since 1924. All information about ringing and the extraction of ringed birds is sent to the Ringing Center of the Russian Academy of Sciences (Moscow). The ringing method made it possible to find out the paths and speeds of birds' flight, the constancy of the return from wintering to old nesting sites, wintering sites, etc.

The variety of birds and their meaning. The Bird class is represented by over 40 squads. Let's take a look at some of them.

Squad Penguin-like. Distributed in the Southern Hemisphere. Birds swim and dive well with the help of their forelimbs converted to flippers. The keel is well developed on the sternum. On land, the body is held vertically. The feathers overlap each other tightly, which prevents the wind from blowing and water penetration. Subcutaneous fat deposits contribute to heat protection. They feed in the sea on fish, molluscs, crustaceans. Nest in colonies. Pairs persist for several years. The hatched chicks are covered with dense and short down. After the breeding season, flocks of penguins with grown-up juveniles wander into the sea. The emperor penguin nests on the coastal ice of Antarctica, its weight reaches almost 40 kg.

Superorder Ostrichiformes. They are characterized by the absence of a keel on the sternum and the ability to fly. The feathers are loose, as the barbs are not interlocked due to the lack of hooks. Powerful hind legs have two or three toes, which is associated with the speed of movement. The African ostrich - the largest living bird - reaches a mass of 75 - 100 kg. Several females (2 - 5) lay eggs weighing about 1.5 kg in a common nest. Male incubates clutch at night, females alternately during the day.

Ostrich-like birds include rhea (South America), emu and cassowary (Australia), kiwi (New Zealand).

Order Storks. They live along the shores of shallow water bodies. A small membrane between the bases of the long toes of storks allows them to walk confidently in swampy places. Birds fly slowly by active or soaring flight. They feed on a variety of animal food, grabbing it with a long, hard, like tweezers, beak. There are 2 - 8 eggs in the nest; chicks are fed by both parents. The detachment includes storks, herons, flamingos, etc.

Storks are migratory birds that winter in Central and South Africa, in parts of South Asia. The white stork is a large bird with large black wings and long red legs. Breeds in single pairs. The stork scares away prey, slowly wandering through forest glades, meadows, and the banks of water bodies. The black stork nests in deep forests. It is listed in the Red Book.

Order Day birds of prey. Distributed in a wide variety of habitats: in forests, mountains, steppes, water bodies, etc. Birds have a short but strong beak with a sharp juvenile beak sharply curved downward. At the base of the beak there is a wax - a patch of bare, often colored skin on which the external nostrils open. The muscles of the chest and hind legs are powerful. The toes end in large, curved claws.

Flight, fast, maneuverable, many species are capable of long soaring. Some types of predators eat only dead animals (vultures, vultures, vultures), others catch live prey (falcons, eagles, hawks, buzzards, harriers).

Most species of birds of prey are beneficial by exterminating murine rodents, ground squirrels, and harmful insects. Carrion-eating species have a sanitary function. The number of birds of prey has declined sharply due to changes in landscapes, poisoning with pesticides and direct extermination. In many countries, birds of prey are protected. The Red Book includes: osprey, snake eagle, great spotted eagle, golden eagle.

Owl squad includes nocturnal birds (owls, eagle owls, owls, barn owls) that inhabit all regions of the globe. They are adapted for hunting at night: they have large eyes directed forward, well-developed hearing, and silent flight. They feed on animal food, mainly on mouse-like rodents. They nest in hollows. The eggs are incubated by the female, the male carries her food. After 3 - 6 weeks, the chicks acquire the ability to fly. Exterminate harmful animals. Owl birds need protection.

Chicken squad includes terrestrial and terrestrial-arboreal birds. They have a short and convex beak, short and wide wings. A bulky goiter is separated from the esophagus. The gizzard is lined with dense ribbed cuticle. To improve the grinding of food, birds swallow pebbles that accumulate in the stomach and play the role of millstones. They feed on plant food - vegetative parts of plants, fruits, seeds, incidentally caught invertebrates. Males are colored brighter than females.

Almost all species of chickens are objects of sport hunting and breeding. Grouse, ptarmigan, black grouse, and in some areas - partridge and gray partridge are of commercial importance. Due to the various economic activities of man, excessive hunting, the number of many species has decreased, and the distribution areas have decreased.

Sparrow squad - the largest order, including about 60% of all living species. Its representatives are distributed throughout all continents, except for Antarctica. They vary greatly in size, appearance and environmental characteristics. Nests are built (sometimes very skillfully) in the branches, crevices of rocks, hollows, on the ground, etc. The chicks hatch blind, naked and poorly pubescent. Most passerines are insectivorous birds.

Larks live in open landscapes (in the field, in meadows, in the steppe). Arrives in early spring. They feed only on the ground on invertebrates and seeds. They nest on the ground. Males often sing in the air.

Swallows nest in river valleys, forest edges, in human settlements. Insects are caught in the air on the fly using a wide mouth. Little people walk on the ground. Some species (city swallow) build stucco nests from lumps of dirt, holding them together with sticky saliva; others dig holes in cliffs (shore martin) or nest in hollows, crevices.

Titmouse nest in hollows, laying 10 to 16 eggs. The female often incubates, and the male feeds her, both parents feed the chicks. They feed on various insects and their larvae, eat berries and seeds. They are easily attracted to cultural landscapes when arranging artificial nests. They are very useful as exterminators of various harmful insects.

Summarizing the characteristics of the main orders of birds, one can draw conclusions about their importance in nature. Due to the high number and high level of vital activity, birds consume a huge amount of plant and animal food every day, significantly affecting natural biocenoses. Their role is especially great in the regulation of the number of insects and small rodents. Often, birds themselves serve as food for other animals.

In addition, birds contribute to the dispersal of plants by spreading seeds. Pecking the juicy fruits of mountain ash, elderberry, lingonberry, bird cherry, blueberry, they fly from place to place and throw out intact seeds along with droppings.

Many birds exterminate pests of cultivated and valuable wild plants. Birds of prey are also useful, destroying small rodents - pests of field crops and spreading infectious diseases (plague, jaundice, etc.).

There are sports and commercial hunting for many wild birds. The collection of eider down, which has great softness and low thermal conductivity, is of great economic importance.

The droppings of sea water birds (pelicans, cormorants, etc.) - guano - are used as a valuable fertilizer.

One of the economically profitable branches of animal husbandry is poultry farming, which provides people with valuable meat products, eggs, and feathers. The poultry industry is on an industrial basis. At large modern poultry farms, the entire process of raising birds (chickens, ducks, turkeys, geese) is mechanized.

Test questions:

What organizational traits are characteristic of birds in connection with their adaptation to flight?

What is the peculiarity of the structure of the digestive system of birds?

What is the characteristic of the double breathing of birds?

What provides warm-blooded birds?

What are the progressive features of bird breeding?

What seasonal phenomena are observed in the life of birds?

What is the role of birds in nature and in human economic activity?

Body shape. Adaptation to flight caused the relative uniformity of the body shape. The body is compact, more or less rounded. The head is small, the neck is long and mobile. The forelimbs - the wings - are folded in a calm state and pressed to the sides of the body. The plumage provides streamlining of the body. Species variations in the size and shape of the beak and head, the length of the neck, the length and shape of the wings and tail, the length of the hind limbs and the shape of their fingers provide, while maintaining the general uniformity of adaptation to different types of movement and nutrition.

Bird sizes vary within small limits; flight capability limits the increase in size. The mass of large flying birds does not exceed 14-16 kg (swans, vultures, bustards) with a wingspan of up to 3-4 m (pelicans, albatrosses). The smallest of the birds are some hummingbirds with a maximum mass of 1.6-2 g. The loss of the ability to fly often leads to an increase in size: the mass of large penguins reaches 40 kg, cassowaries and African ostriches - 80-100 kg. Some of the extinct running birds reached a mass of 300-400 kg (epyornis, moa).

Leather and its derivatives. The skin of birds is thin, dry, practically devoid of skin glands. The surface layers of cells of the epidermal layer are keratinized. The connective tissue layer of the skin is subdivided into a thin, but rather dense skin itself, in which blood vessels pass, the ends (points) of the contour feathers are strengthened and bundles of smooth muscle fibers that change the position of the feathers are located, and subcutaneous tissue is a loose layer directly adjacent to the trunk muscles; it stores fat reserves. The only cutaneous gland, the coccygeal gland, lies on the caudal vertebrae. It produces a fat-like secretion that is secreted through the ducts when the birds press down on the gland with their beak. Birds lubricate feathers with this secret, which helps to maintain their elasticity and partly increases the water-repellent properties of plumage. The sebaceous secretions of the coccygeal gland under the influence of sunlight are converted into vitamin D, which birds ingest when cleaning the feathers. The coccygeal gland is well developed in most birds, both aquatic and terrestrial (anseriformes, chickens, etc.); only in a few terrestrial and aquatic birds it is poorly developed (cormorants, herons) or absent (ostrich-like, bustards, some parrots).

The growths of the keratinizing epidermal layer of the skin form the stratum corneum of the beak - rhamfotek. Reptilian-type horny scales cover the fingers, tarsus, and sometimes part of the lower leg. The last phalanges of the toes are covered with horny claws. In males of some birds (for example, pheasants), a bony outgrowth is formed on the tarsus, covered with a sharp horny sheath - a spur. The feather cover, specific for birds, is also horny formations of the epidermal layer of the skin.

Basic pen type- contour pen. It consists of a strong and elastic horny trunk, on the sides of which there are soft outer and inner webs. The part of the trunk to which the fans are attached is called the rod; it has a four-sided shape in diameter. The lower, fanless part of the trunk is called a point and has a rounded cross-section; the base of the quill is immersed in the skin and is fixed in the feather bag. Each fan is formed by elongated horny plates extending from the lateral sides of the rod - first-order barbs, from which, in turn, extend numerous thinner second-order barbs (barbs) with small hooks located on them. The hooks, interlocking with adjacent barbs, form an elastic fan plate. If, for example, upon impact, the hooks disperse and the fan "breaks", the bird, adjusting the feather with its beak, will force the hooks to interlock again, and the feather structure will be restored. Usually, at the very bottom of the feather, the barbs are thinner and fluffy, without hooks; this is the downy part of the fan, the function of which is to keep a layer of air near the skin. In sedentary birds, the winter feather has a more developed down part than the summer one. In some birds (chicken, etc.), an additional rod leaves the ventral surface of the rod at the level of the lower edge of the fan, the soft branching barbs of which also do not have hooks. The development of downy additional rods increases the heat-insulating qualities of the feather.

Diverse bird coloring It is provided both by the accumulation of pigments in the cells of the feather during the period of its formation, and by the microscopic features of the feather structure. The main types of pigments are melanins and lipochromes. Lumps and grains of melanins accumulating in the horny cells cause black, brown and gray coloration. Lipochromes in the form of fatty drops or flakes lie in the horny substance, providing red, yellow and green coloration. The combination of different pigments in the same area of ​​the feather complicates the coloring. The white color is due to the colorless horny mass of the feather filled with air. The metallic luster, which is characteristic of the feathers of many birds, is created due to the interference of light in the outer membranes of the horny cells. The pigments that color the feather increase its mechanical strength. The color of the plumage has a variety of meanings: it facilitates the meeting of individuals of the same species, prevents interspecific collisions, often makes the bird unobtrusive in its usual habitat, etc.

Contour feathers, covering the entire body of the bird, are strengthened in the skin on special fields - pterilia, separated by apteria - areas of the skin on which feathers do not grow. This arrangement of tiled feathers overlapping each other makes it possible to cover the entire body with a minimum number of feathers. Only a few birds, mostly non-flying (ostrich-like, penguins), have feathers evenly distributed over the entire surface of the skin. Long and extra strong feathers form the plane of the wing; they are called flywheels. The primary flight feathers are attached to the posterior edge of the skeleton of the hand, the secondary ones to the posterior superior side of the ulna. The flight feathers are arranged so that the outer fan covers only part of the wider inner fan of the adjacent feather. When the wing is lowered, the feathers form a solid plane, pressing on the air. When the wing is raised, the flywheels turn slightly and gaps are formed between them through which air passes. The long and strong feathers that form the plane of the tail are called tail feathers.

Down feathers lie under the outline feathers; they have a thin shaft, and the barbs do not have hooks, so a linked fan is not formed. Down is a downy feather with a sharply shortened shaft and long, heavily pubescent beards that extend in a bunch from the end of the ochin. Down and downy feathers either evenly cover the entire body (anseriformes, copepods, etc.), or are located only along the apteria (herons, owls, many passerines). Down and feathers provide thermal insulation. Many birds have threadlike feathers all over their bodies with a thin trunk and sparse short beards. They serve as sensors that signal air currents under the feathers. In the corners of the mouth, many birds have bristles; these are feathers with an elastic shaft that have lost their beards. They perform a tactile function, and in some species that catch small prey on the fly (nightjars, swallows, swifts), they increase the size of the mouth opening.

Pen development. As a result of the proliferation of cells of the epidermis and cutis, a tubercle forms on the skin (it is similar to the rudiment of reptile scales), which gradually grows in the form of a backward outgrowth, the base of which deepens into the skin, forming a feather sheath. The connective tissue part of the outgrowth turns into a papilla of the growing feather penetrated with blood vessels. At the same time, the growing epidermal layer differentiates into a thin horny cap, covering the growing feather, and from the intensively dividing and gradually keratinizing underlying cells, a rod with barbs extending from it is formed. As the feather grows, the horny cap surrounding it gradually peels off, and the beards straighten, forming a fan. A fully grown feather is a dead formation held by the walls of the vagina and the muscle bundles of the corium, which are tightly attached to the quill. Their reduction allows you to change the position of the feather (fluff or, conversely, press the plumage). The papilla dries up; from him in the depths of the feather remains only a filmy darling.

Over time, feathers wear out and fade, their mechanical and thermal insulation properties deteriorate. Therefore, there is a periodic change of feather - molt. Full molt with a change of all feathers usually takes place at the end of summer, after the end of reproduction. Usually, this does not significantly impair the flying ability of birds.

However, in some groups (anseriformes, shepherdesses, cranes, etc.), the contour feathers change over the body gradually, and the flight feathers and tail feathers fall out simultaneously about their coverts, and the bird loses its ability to fly (small ducks - for about 20 days, swans - almost for 1.5 months); molting birds keep in hard-to-reach places.

Some species have not one, but two molts per year. The second usually occurs in early spring and does not capture all plumage: tail and flight feathers do not change. The presence of two molts provides the possibility of seasonal changes in color and quality of plumage. Thus, during the autumn molt, grouse develops longer cover feathers with a more developed down part of the fan and with a long, fluffy accessory shaft, which significantly increases the insulating qualities of the winter plumage as compared to the summer plumage. Sedentary small birds in winter plumage have more feathers than summer ones, which also provides better thermal insulation in winter: for example, siskins in winter plumage have 2,100-2400 feathers, and in summer ones - about 1,500.

The motor system and the main types of movement. The movements of birds are diverse: walking, jumping, running, climbing, swimming, diving, flying. They are provided both by changes in the musculoskeletal system, and by transformations of other organ systems that coordinate movements and orientation in space, creating the necessary energy reserves. A peculiar feature of the skeleton of birds is the well-expressed pneumaticity of the bones. Flat bones have a spongy structure, retaining great strength with a small thickness. Tubular bones are also thin-walled, and the cavities inside them are filled partly with air and partly with bone marrow. These features provide increased strength to individual bones and make them noticeably lighter. However, it is necessary to pay attention to the fact that the total mass of the skeleton is 8-18% of the body weight of birds - about the same as in mammals, in which the bones are thicker, and there are no air cavities in them. This is explained by the fact that in birds the lightening of the bones made it possible to dramatically increase their length (the length of the skeleton of the leg, and especially the wing, is several times greater than the length of the body), without noticeably increasing the total mass of the skeleton. Like other higher vertebrates, the skeleton of birds is subdivided into an axial skeleton and associated thorax, skull, skeleton of limbs and their belts.

Axial skeleton- the vertebral column is divided into five sections: cervical, thoracic, lumbar, sacral and caudal. The number of cervical vertebrae is variable - from 11 to 23-25 ​​(swans). As in reptiles, the first vertebra - the atlas, or atlas - has the shape of a bony ring, and the second, the epistrophy, is articulated with it by a dentate process; this allows the head to move in relation to the neck. The rest of the cervical vertebrae of birds are of a heterocoleal type, the long body of each vertebra in front and behind has a saddle-shaped surface (in the sagittal section, the vertebrae are opistocoelous, and in the frontal section, they are procellular). The articulation of such vertebrae ensures their significant mobility relative to each other in the horizontal and vertical planes. The strength of the vertebral joints is enhanced by the presence of articular processes at the bases of the upper arches, which form sliding joints between themselves. The cervical ribs of birds are rudimentary fused with the cervical vertebrae, forming a channel through which the vertebral artery and the cervical sympathetic nerve pass. Only the last one or two cervical ribs articulate with the cervical vertebrae movably, but they do not reach the sternum. The features of the cervical vertebrae, together with the complexly differentiated cervical muscles, allow birds to freely turn their heads by 180 °, and some (owls, parrots) and 270 °. This makes possible complex and quick movements of the head when grasping mobile prey, cleaning plumage, building a nest; in flight, it allows, by bending or unbending the neck, within certain limits, to change the position of the center of gravity, facilitates orientation, etc.

The thoracic vertebrae in birds are 3-10. They fuse with each other, forming the dorsal bone, and are connected with a very tight joint to the complex sacrum. Due to this, the trunk section of the axial skeleton becomes motionless, which is important during flight (body vibrations do not interfere with the coordination of flight movements). The ribs are movably attached to the thoracic vertebrae. Each rib consists of two sections - dorsal and abdominal, movably articulating with each other and forming an angle, apex directed backward. The upper end of the dorsal rib is movably attached to the transverse process and the body of the thoracic vertebra, and the lower end of the abdominal region to the edge of the sternum. The movable articulation of the dorsal and abdominal parts of the ribs with each other and their movable connection with the spinal column and the sternum, along with the developed costal muscles, provide a change in the volume of the body cavity. This is one of the mechanisms of breathing intensification. The strength of the chest is enhanced by the hook-shaped processes, fixed on the dorsal regions and overlying the subsequent rib. The large sternum looks like a thin, wide and long plate on which all birds (except ostrich-like) have a high sternum keel (crista sterni). The large size of the sternum and its keel provide a place for the attachment of powerful muscles that move the wing.

All lumbar, sacral (there are two of them) and part of the caudal vertebrae immovably grow together with each other into a monolithic bone - a complex sacrum (synsacrum). In total, it includes 10-22 vertebrae, the boundaries between which are not visible. The bones of the pelvic girdle are immovably fused with the complex sacrum. This ensures the immobility of the trunk and provides solid support for the hind limbs. The number of free caudal vertebrae does not exceed 5-9. The last 4-8 caudal vertebrae merge into the laterally flattened coccygeal bone of the pygostyle, to which the bases of the tail feathers are attached in a fan. The shortening of the tail section and the formation of pigostyle provide strong support for the tail while maintaining its mobility. This is important, since the tail not only serves as an additional bearing plane, but also participates in flight control (like the brake and rudder).

Bird skull similar to the skull of reptiles and can be attributed to the diapsid type with a reduced upper arch. The tropibasal skull (the orbits are located in front of the brain), formed by thin spongy bones, the boundaries between which are clearly visible only in young birds. This, apparently, is due to the fact that the connection with sutures is impossible due to the small thickness of the bones. Therefore, the skull is relatively light. Its shape is also peculiar in comparison with reptiles: the volume is sharply increased. the cerebral box, the eye sockets are large, the jaws are devoid of teeth (in modern birds) and form a beak. The displacement of the foramen magnum and occipital mucosa to the bottom of the skull increases the mobility of the head relative to the neck and trunk.

The foramen magnum is surrounded by four occipital bones: the main (basioccipitale), two lateral (occipitale laterale) and the upper (supraoccipitale). The main and lateral occipital bones form a single (like in reptiles) occipital condyle, articulating with the first cervical vertebra. The three ear bones surrounding the auditory capsule merge with the adjacent bones and between themselves. In the middle ear cavity there is only one auditory ossicle - the stapes. The sides and roof of the cerebral box form paired integumentary bones: scaly, parietal, frontal and lateral wedge-shaped (laterosphenoideum). The bottom of the skull is formed by the integumentary main sphenoid bone, which is covered by the integumentary main temporal bone (basitemporale), and the coracoid process of the parasphenoid (rostrum parasphenoidei). At its front end there is a coulter, along the edges of which choanas are located.

The upper part of the beak - the beak - is formed by highly overgrown and fused premaxillary bones. The ridge of the beak, reinforced by the nasal bones, connects to the frontal bones and the anterior wall of the orbit, formed by the overgrown middle olfactory bone (mesethmoideum). The maxillary bones, which make up only the posterior part of the beak, merge with the palatine bones by processes. A thin bony bar, consisting of two fused bones - the zygomatic and square-zygomatic - grows to the posterior-outer edge of the maxillary bone. This is a typical lower arch of the diapsid skull, limiting the orbit and temporal fossa from below. The square-zygomatic bone articulates with the square bone, the lower end of which forms an articular surface for articulation with the lower jaw, and the elongated upper end is connected by a joint to the squamous and anterior auricular bones. The palatine bones with their ends lie on the coracoid process of the parasphenoid and are connected by a joint to the paired pterygoid bones, which in turn are connected by a joint to the square bones of the corresponding side.

This structure of the bony palate is important for the kinetic (mobility) of the beak inherent in most birds. With the contraction of the muscles connecting the forward-directed orbital process of the square bone with the wall of the orbit, the lower end of the square bone shifts forward and shifts both the palatine and pterygoid bones (their connection with each other can slide along the coracoid process), and the square-zygomatic and zygomatic. The pressure along these bony bridges is transmitted to the base of the beak and due to the bending of the bones in the region of the "bridge of the nose" the apex of the beak moves upward. In the inflection zone of the beak, the bones are very thin, and in some species (geese, etc.) a joint is formed here. With the contraction of the muscles connecting the skull to the lower jaw, the apex of the beak moves downward. The mobility of the bony palate in combination with complexly differentiated masticatory muscles provide a variety of finely differentiated beak movements when grasping prey, cleaning plumage, and building nests. Probably, the mobility of the neck and the adaptation of the beak to a variety of movements contributed to the transformation of the forelimbs into wings, since they replaced some of the secondary functions performed by them (assistance in capturing food, cleaning the body, etc.).

The lower part of the beak - the mandible or lower jaw - is formed by the fusion of a number of bones, of which the larger ones are dental, articular and angular. The jaw joint is formed by the articular and square bones. The movements of the mandible and mandible are very clearly coordinated due to the differentiated system of the masticatory muscles. The sublingual apparatus consists of an elongated body supporting the base of the tongue and long horns. Some birds, such as woodpeckers, have very long horns that go around the entire skull. With the contraction of the hyoid muscles, the horns slide along the connective tissue bed and the tongue moves out of the oral cavity almost to the length of the beak.

The skeleton of the forelimb, which has turned into a wing in birds, has undergone significant changes. The powerful tubular bone - the shoulder - has a flattened head, which significantly limits rotational movements in the shoulder joint, ensuring the stability of the wing in flight. The distal end of the shoulder articulates with two bones of the forearm: a straighter and thinner radial and a more powerful ulnar, on the posterior side of which tubercles are visible - the places of attachment of the points of the secondary flight feathers. From the proximal elements of the wrist, only two small independent bones are preserved, which are connected by ligaments to the bones of the forearm. The bones of the distal row of the wrist (carpus) and all bones of the metacarpus (metacarpus) merge into a common metacarpal-carpal bone (carpometacarpus), or buckle. The skeleton of the fingers is sharply reduced: only two phalanges of the second toe are well developed, continuing the axis of the buckle. Only one short phalanx is preserved from the first and third toes. The primary flywheels are attached to the buckle and to the phalanges of the second toe. Several winglet feathers are attached to the phalanx of the first toe.

The transformation of the hand (buckle formation, finger reduction, low joint mobility) provide solid support for the primary swing arms, which experience the greatest loads in flight. The nature of the surfaces of all joints is such that it provides easy mobility only in the plane of the wing; the possibility of rotational movements is sharply limited. This prevents the wing from turning, allows the bird to effortlessly change the wing area in flight and fold it at rest. Connecting the wrist fold with the shoulder joint, a fold of skin - the flying membrane (patagium) - forms an elastic front edge of the wing, smoothing the elbow fold and preventing the formation of air turbulence here. The wing shape characteristic of each species is determined by the length of the skeletal elements and the secondary and primary flywheels.

Flight attachments clearly expressed in the girdle of the forelimbs. Powerful coracoids with extended lower ends are firmly connected by sedentary joints with the anterior end of the sternum. The narrow and long shoulder blades fuse with the free ends of the coracoids, forming a deep glenoid cavity for the head of the shoulder. The strength of the bones of the shoulder girdle and their strong connection with the sternum provide the wings with support in flight. Elongation of the coracoids increases the area of ​​attachment of the wing muscles and carries the shoulder joint forward, to the level of the cervical vertebrae; this makes it possible to lay the wing on the side of the body at rest and is advantageous aerodynamically, because in flight the bird's center of gravity is on the line connecting the centers of the wing areas (stability is ensured). The clavicles grow together into a fork (furcula), located between the free ends of the coracoids and acting as a shock absorber, softening the jolts during wing flaps.

The hind limbs and pelvic girdle undergo transformations associated with the fact that when moving on land, all the weight of the body is transferred to them. The skeleton of the hind limb is formed by powerful tubular bones. The total length of the leg, even in the "short-legged" species, exceeds the length of the body. The proximal end of the thigh ends with a rounded head articulating with the pelvis, and at the distal end, the relief surfaces form a knee joint with the bones of the lower leg. It is strengthened by the lying in the muscle tendon knee cap... The main element of the tibia is the bone complex, which can be called the tibia-tarsus, or tibiotarsus, since the upper row of tarsal bones grows to the well-developed tibia (tibia), forming its distal end. The fibula is highly reduced and grows to the upper part of the outer surface of the tibia. Its reduction is associated with the fact that in most birds all elements of the limb move in one plane, rotational movements in the distal part of the limb are limited.

The distal (lower) row of bones of the tarsus (tarsus) and all bones of the metatarsus (metatarsus) merge into a single bone - the tarsus, or metatarsus (tarsometatarsus); an additional lever appears, increasing the length of the stride. Since the movable joint is located between two rows of tarsal elements (between the bones fused with a large tibia, and the elements included in the tarsus), then it, like reptiles, is called intertarsal. The phalanges of the fingers are attached to the distal end of the tarsus.

Like all terrestrial vertebrates, the pelvic girdle of birds is formed by fused three pairs of bones. The wide and long ilium fuses with the complex sacrum. The ischium grows to its outer edge, with which the rod-shaped pubic bone grows together. All three bones participate in the formation of the acetabulum, into which, forming the hip joint, the femoral head enters. The pubic and ischial bones in birds do not fuse with each other along the midline of the body; such a basin is called open. It makes it possible to lay large eggs and, perhaps, contributes to the intensification of respiration, without limiting the mobility of the abdominal wall in the pelvic region.

The large pelvic surface and its strong connection to the axial skeleton provide support for the hind limbs and create opportunities for the attachment of powerful leg muscles. Long strong bones of the extremities, the sharp relief of their articular surfaces, along with well-developed and differentiated leg muscles provide intensive movement in a variety of conditions.
The musculature of birds is more differentiated, and its relative mass is greater than that of reptiles. This is due to the greater mobility of birds and the variety of their movements. The compactness of the body, due to the requirements of aerodynamics, is largely achieved by the fact that the most powerful muscles that move the limbs are located on the trunk, and their tendons go with the limbs. The strong development of the ligaments strengthens the connection of the individual elements of the skeleton. The muscles of the neck are very complex, providing high mobility of the head, which is important both when grasping Prey, and when orienting, and in flight.

Of the muscles of the forelimb, two are primarily worth mentioning. The subclavian muscle (musculus subclavius) is attached to the coracoid, body and crest of the sternum, and its tendon ends at the head of the shoulder; contraction of this muscle raises the wing. Above it lies, attaching itself to the sternum and its keel, to the coracoid and the coracoid-clavicular ligament, the pectoralis major muscle (m. Pectoralis major), lowering the wing in flight; her tendon is also attached to the head of the shoulder. Both pectoralis major muscles make up from 10 to 25% of the total weight of the bird and exceed the mass of the subclavian muscles by 3-20 times. These muscles are especially large in birds flying in a swift, maneuverable flight. In addition, the work of the wing in flight is controlled by several dozen smaller muscles located on the trunk, shoulder and forearm.

More than 30 muscles perform the movements of the hind limbs. The larger ones are attached with wide bases to the bones of the pelvis, the small muscles are located on the thigh and lower leg. The deep flexor of the fingers (m.flexor digitorum perforans) located on the posterior surface of the lower leg forms a tendon that passes along the posterior side of the intertarsal joint and tarsus, and then divides into four branches and ends on the lower surface of the terminal phalanges of the fingers. The surface of the terminal tendons and the bottom of the wide connective tissue sheaths, along which they move, have transverse ribbing. When the bird sits on a branch and squeezes its fingers, under the pressure of its mass, the tendons are pressed against the wall of the vagina, and their ribs interlock: the fingers remain in a compressed state when the muscle relaxes. To open this "automatic lock", you need to contract the muscles - the extensors of the fingers. This allows the birds to sleep sitting on a branch with relaxed muscles.

Respiratory movements of the chest are carried out using the intercostal and other muscles of the body walls. Several muscles move the tail. Compared to reptiles, birds have better developed subcutaneous musculature, which makes it possible to change the position of feathers in large areas of the body. Small muscle bundles of the corium change the position of individual feathers.

Birds are characterized by the accumulation of myoglobin in the muscles, which makes it possible to create a reserve supply of oxygen, utilized during the period of intensive work. The highest concentration of myoglobin was found in the pectoralis major muscle, the musculature of the gizzard and heart. The concentration of muscle hemoglobin is higher in birds flying in active flight, in diving birds and birds in highlands. In all cases, however, the concentration of hemoglobin in the blood is higher than in the muscles.

Climbing and jumping in the branches with the help of the hind and partly forelimbs and the use of wings for gliding - these are, apparently, the main ways of movement of primitive ancient birds. And now most of the species are to some extent associated with the crowns of trees and bushes. In the branches, birds usually move by jumping, sometimes helping with single flaps of their wings. The usual type of paw structure for them - three toes forward, one back - allows them to firmly grip the branches. Further specialization to the arboreal lifestyle is often accompanied by a change in the structure of the paw - two toes are directed forward, two backward, which probably makes it even easier to hold on to the branches. Perfectly climbing in crowns, parrots use a powerful beak for grasping. Due to a sharp increase in the muscles of the legs, the development of strong fingers with sharp claws, many, especially small, bird species have mastered climbing vertical trunks (nuthatches, pikas, etc.) and along rocks. Strong paws with powerful fingers and sharp claws and a strong tail, which serves as an additional support, allow woodpeckers not only to climb vertical trunks, but, holding in one place, gouge bark and wood.

Many species of arboreal birds also collect food on the ground. At the same time, small species, as in the branches, jump (sparrows, etc.), while others walk and run, alternately rearranging their legs (white wagtail, rook, crow, etc.). Adaptation to a terrestrial lifestyle is often accompanied by shortening of the fingers, especially those directed backward (sometimes it is reduced), lengthening of the tarsus. The best bird runners are ostrich-like birds that have lost their ability to fly. The three-toed South American rhea and the two-toed African ostrich can run at speeds over 50 km / h. In the inhabitants of swamps and the shores of water bodies (egrets, shepherdesses, waders, etc.), the lengthening of the tarsus and tibia allows wandering in shallow water without wetting the plumage, and long thin fingers do not allow to fall through on viscous soil. In the capercaillie, hazel grouse and other black grouse, horny spines grow on the sides of the fingers during the autumn molt, increasing the support area and reducing sinking into the snow, and in white partridges, long feathers grow on the fingers, turning the paw into a ski - a snowshoe. Many swimming birds walk well on land (seagulls, etc.); some good divers have legs far back and they can hardly move on land (loons, toadstools). Some well-flying species (swallows, bee-eats, swifts) walk little and poorly.

Having high organization and able (with rare exceptions) to fly. Birds are ubiquitous on earth, therefore they play an important role in the formation of many ecosystems, and are also part of the economic activity of people. Modern science about 9,000 species of birds are known today. In different periods of the past, there were much more of them.

The following general for birds characteristics:

1. Streamlined torso... The forelimbs are adapted for flight, not walking, therefore they have a special structure and are called wings. Hind limbs of birds serve for walking and as a support for the torso.
2. Skeleton of birds has a small thickness, the tubular bones have cavities with air, which lighten the weight of the birds and contribute to less weight. This allows the birds to stay in the air longer. Skull in birds has no seams, it is formed from spliced ​​bones. The spine is not highly mobile - only the cervical spine is mobile.
   There are two structural features of the skeleton, characteristic only of birds:

   - Tarsus- a special bone that helps birds to increase the width of their stride;
   - Keel- the bony protrusion of the sternum of birds, to which the flight muscles are attached.

3. Bird skin have almost no glands, dry and thin. There is only coccygeal gland, which is located in the tail section. Grow from the skin feathers- these are horny formations that create and maintain a microclimate in birds, and also help to fly.
4. The muscular system of birds includes many different types of muscles. The largest muscle group is flying pectoral muscles... These muscles are responsible for lowering the wing, that is, for the flight itself. Cervical, subclavian, subcutaneous, intercostal muscles and leg muscles are also well developed. The motor activity of birds is differentiated: they can walk, run, jump, swim, climb.
   There is also two types of bird flight: soaring and waving... Most bird species can fly great distances ( bird migration).
5. Respiratory organs of birds- lungs. Birds double breathing- this is when, in flight, the bird can breathe both at the entrance and on the exhale, without suffocating in this way. When the bird inhales, the air enters not only the lungs, but also air bags... From the air sacs, it enters the lungs when you exhale.
6. Birds heart four-chamber, capable of completely separating blood into arterial and venous... The heart beats rapidly, washing the body with pure arterial blood. High motor intensity is inextricably linked with a high body temperature, which is maintained at about +42 o C. Birds are already warm-blooded animals with a constant body temperature.
7. Digestive system of birds has its own characteristics, which are associated with the digestion of large volumes of often rough food (grains, vegetables, fruits, insects, etc.), as well as with the facilitation of the mass of the gastrointestinal tract. It is with the latter circumstance that the absence of teeth in birds, the presence of goiter and the muscular section of the stomach, as well as the shortening of the hind gut, are associated. So, birds have no teeth, so beak and tongue are involved in getting food. Goiter in birds served for mixing the food entering it, after which it is sent to the stomach. IN muscular stomach food is ground and mixed with each other and with gastric juices.
8. Excretory organs in birds, as well as the products of the final decay of urea in birds coincide with those in reptiles, with the difference that birds do not Bladder to reduce body weight.
9. Bird brain divided into 5 sections. The greatest mass, respectively, the best development, have two hemispheres of the forebrain that have a smooth bark. The cerebellum is also well developed, which is associated with the need to have excellent coordination and complex forms of behavior. Birds orient themselves in space with the help of sight and hearing.
10. The birds are dioecious animals, which can already be observed sexual dimorphism... Females have a left ovary. Fertilization takes place inside, bird development- direct. Most bird species build nests in which they lay their eggs. The female incubates eggs throughout the entire time until the chicks hatch, which are then fed and taught to fly. Chicks can be brood and nesting - depending on how well the chicks hatching from the eggs are well developed.