Bird Class (Aves) A \u200b\u200bgeneral description of the class. Feathers of birds

At present, about 8.6 thousand species of birds live on Earth. In their structure, birds are very similar to reptiles and represent a progressive branch, the evolution of which went along the path of adaptation to flight.

Birds are two-legged higher animals, whose forelimbs turned into wings, the body is covered with feathers, the body temperature is constant and high.

The whole organization of birds is adapted to flight conditions. The body of birds is compact, the skeleton is extremely lightweight; spreading wings and tail form an area much larger than the area of \u200b\u200bthe body.

In the structure of the body of birds, one can note features characteristic not only for birds, but also signs common with reptiles. So, in the skin of birds there are no glands, with the exception of the coccygeal gland above the root of the tail. Some birds also lack this gland.

We will consider the characteristic features of birds on the example of a pigeon.

All domestic and semi-domestic breeds of pigeons living in cities and villages are descended from a wild bluish pigeon. Domestic pigeons are kept in packs and settle on various buildings. They feed on seeds, green herbaceous plants, bread and other food debris.

The integument of birds

Skin of birds  dry and very thin:

• On the beak, the skin forms horn covers;
• on the limbs - horny scales;
• on the fingers are claws.

Derivatives of the skin are feathers phylogenetically associated with scaly formations (this is indicated by the similarity in the development of feathers and scales in the early stages).

Feathers of birds. Structure and function

The body of all birds is covered with feathers.. Distinguish between contour and feathers. Each contour feather has a narrow solid rod, or trunk, and elastic plates on the sides that make up the fan. That part of the rod that does not have a fan is called ochin.

Contour feathers protect the body from rain and wind. They are divided into flywheel, integumentary and steering. The largest - feathersleaning against each other, they form a fairly solid flying surface of the wing. Strength contour feathers  due to the fact that the fan is composed of separate horn barbs (first and second order). The first-order barbs are attached to the trunk in parallel - one next to the other. Thinner beards of the second order extend from each beard on both sides. They lean on adjacent beards, are fastened with them with microscopic hooks.

In most species of birds under the contour feathers are located downy. They differ from the contour in that they are plowed loose, soft and do not form a continuous plate. Feathers have a very short shaft with a bunch of first-order barbs on top. Between the feathers a lot of warm air is trapped. Contour feathers in the tail act as a rudder during flight, they are called so helmsmen.

Shedding periodically occurs in birds - new ones grow on the site of old fallen feathers.

In the skin of a pigeon, like many other species of birds, there is only one coccygeal gland, which is located at the base of the tail on the dorsal side. In chickens and other species of land birds, this gland is underdeveloped. It is especially developed in waterfowl. The coccygeal gland secrets a secret that birds use feathers to grease feathers.

Skeleton and Musculature

The bones of the skeleton are filled with air and are very light. The skull is characterized by complete fusion of all bones until the sutures disappear, extreme lightness and large eye sockets.

The jaws of birds are represented by a light beak, devoid of teeth.

Spinal column  has a large number of vertebrae that make up five departments. Numerous (up to 25) cervical vertebrae are extremely mobile, the thoracic vertebrae are almost motionless, and the lumbar and sacral spliced \u200b\u200btogether. This creates the compactness of the body needed during flight. As a result of the fusion of the lumbar, sacral, and parts of the caudal vertebrae both with each other and with the pelvic bones, a complex sacrum is formed. It serves as a support for the hind limbs, bearing the weight of the body.

Attached to the thoracic vertebrae ribs. They consist of two parts, movably connected to each other. The upper part of each of the ribs is movably connected to the spinal column, the lower - to the sternum. On the upper part of each of the ribs there are hook-shaped processes overlapping adjacent posterior ribs. This ensures the integrity of the chest while maintaining the mobility of the sternum.

In most species of birds, the sternum has a high longitudinal keel, used to attach the muscles that make the wings move. Three paired bones enter the belt of the forelimbs of birds: crows, shoulder blades and clavicles. The collarbones fuse to form a little fork.

Forelimbs  - wings - fully adapted to flight. Their elements, typical of a five-fingered limb, are partially reduced and modified. Their skeleton includes the humerus, ulna and radius, one complex bone from the fused bones of the hand and the bones of only three fingers.

Skeleton legs  birds make up a massive femur, shin, consisting of two fused bones, foregrip and finger bones. The tarsus is formed by the fused bones of the foot. Most birds (and the dove) have four fingers, one of them is facing back, and three are forward.

The muscles are well developed. V. connection with the adaptation of birds to flight is characterized by the presence of huge pectoral muscles, which are more developed, the better the bird flies. The abdominal muscles are weaker than the pectoral muscles. Muscles of the neck and limbs are developed.

With a high organization and the ability (with rare exceptions) to fly. Birds are ubiquitous on the earth, therefore, they play an important role in the formation of many ecosystems, and are also part of human activities. Modern science knows about 9,000 species of birds existing today. In different periods of the past, there were much more.

The following can be distinguished generalfor birds characteristics:

1. Streamlined body shape. The forelimbs are adapted for flight rather than 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, tubular bones have cavities with air, which facilitate the weight of 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 of fused 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:

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

3. The skin of birds  almost no glands, dry and thin. There is only coccygeal gland, which is located in the tail section. From the skin grow feathers- These are horn 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 are flying pectoral muscles. These muscles are responsible for lowering the wing, that is, for the flying process itself. The cervical, subclavian, subcutaneous, intercostal muscles and muscles of the legs are also well developed. The motor activity in birds is differentiated: they can walk, run, jump, swim, climb.
      Also exists two types of bird flights: soaringand waving. Most species of birds can fly vast distances ( bird migration).
5. Respiratory organs of birds  - lungs. In birds double breath  - this is when in flight a bird can breathe both at the entrance and exhale, without suffocating in this way. When a bird inhales, air enters not only the lungs, but also air bags. From the air sacs it enters the lungs upon exhalation.
6. Heart in birds  four-chamber, capable of completely separating blood into arterialand venous. The heart beats fast, washing the body with pure arterial blood. High motor intensity is inextricably linked with high body temperature, which is maintained at about +42 ° C. Birds are already warm-blooded animals with a constant body temperature.
7. The digestive system of birds  It has its own characteristics, which are associated with the digestion of large volumes of often coarse 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 muscle of the stomach, and also the shortening of the hind gut are associated. So, the birds have no teeth, so beak and tongue participate in the writing. Goiter in birds  served to mix the food entering it, after which it goes into the stomach. AT muscle of the stomach  food is ground and mixed with each other and with gastric juices.
8. Excretory organs in birds, as well as products of the final decay of urea in birds coincide with those in reptiles, with the difference that birds have no bladder  to reduce body weight.
9. Brain of birds  divided into 5 departments. The greatest mass, respectively, the best development, have two hemispheres of the forebrainthat have smooth bark. The cerebellum is also well developed, which is associated with the need to have excellent coordination and complex forms of behavior. Birds are oriented in space with the help of sight and hearing.
10. Birds are dioecious animalswhich can already be observed sexual dimorphism. Females have a left ovary. Fertilization takes place inside, bird development  - direct. Most bird species make nests where they lay their eggs. The female hatches 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 hatching from eggs is well developed.

TOPIC: “Type of chordates. Classes of birds. "

PLAN

1. General characteristics of the class of birds. Origin of birds

2. The external structure in connection with the lifestyle

3. The internal structure of birds

4. The importance of birds

General characteristics of the class of birds

From the archosaurs originates pseudosuchia, they occupied all land areas, but even they cannot be considered direct ancestors of birds. Immediate ancestors of birds have not yet been established. In the last century, namely in the Jurassic deposits, a feather imprint was found first, and then two relatively complete skeletons. According to one of them, in 1861, the German paleontologist G. Meyer made a description of “an animal covered with feathers,” an imprint of the skeleton of which was found in lithographic slates in Bavaria. The poultry received the scientific name Archeopteryx. An analysis of the structure of archeopteryx provides a basis for their lifestyle. These were woody climbing animals that could plan to flip, but not fly. This is evidenced by a weak skeleton of the forelimbs, a weak sternum without a keel, and a smooth surface of the wing bones. Judging by the structure of the pelvis, they laid small eggs, the size of 1 \\ 4 chicken eggs. Weak teeth speak of eating insects and fruits. One way or another, 170 million years ago, real birds appeared. In birds, the nervous system and sensory organs are improved under the influence of adaptations in behavior. Redox processes are accelerated - all systems change, the level of metabolism rises. As a result, warm-bloodedness appears and as a result there are integuments that protect against hypothermia.

Ornithology- A science that studies the life and structure of birds. The modern fauna is approximately 8 thousand 600 species of birds. We have 750 or 8.5%. These are flying land vertebrates, the whole organization is connected with flight - forelimbs - wings, except for ostriches - up to 80-90 km / h.

The main signs of birds

1. The body is covered with feathers that perform a heat-insulating function and provide a streamlined body.

2. The transformation of the forelimbs into wings, which was accompanied by the restructuring of the skeleton and muscles of the limbs and shoulder girdle.

3. The transformation of the skeleton and muscles of the hind limbs and pelvic girdle provided the opportunity for bipedal walking on a solid substrate and swimming.

4. The complete separation of the large and small circles of blood circulation contributed to a better supply of oxygen and nutrients to the tissues. There was a 4-chamber heart. The right aortic arch is preserved, and the left is reduced.

5. There was pneumatization of the bones, which increased their strength.

6. There was an intensification of breathing due to the system of air sacs associated with the lungs.

7. The increased, but constant body temperature allowed the birds to develop areas with a cold climate.

8. Females developed a reduction in the right ovary and oviduct.

9. In many ways, they are similar to reptiles (horn cover was found - foregut, almost complete absence of skin glands, 1 condyle, skull of the dioxide type, arterial blood in the right aortic arch, embryonic development and structure of the genitourinary system).

In 1679 The Italian scientist J. Boreli in his work "Animal Life" noted the most important features of the anatomy of birds associated with flight.

Features of adaptation of birds to flight:

· The transformation of the forelimbs into wings;

· Streamlined body, covered with feathers, tiling in the wing;

· The formation of the sternum in the form of a keel, with powerful muscles that control the wings;

· Double breathing for intense metabolism

Lightweight skeleton (hollow bones)

· Weight loss due to the absence of the bladder, one ovary, teeth, rectum

· The presence of high visual acuity and progressive development of the brain, in particular the cerebellum. Among the birds there are no purely aquatic, purely terrestrial species. In connection with the flight in a certain environment, the size of the birds also varies.

The number of individuals of individual bird species is different. There are birds that are very numerous. Since 1600, 90 species of birds have become extinct; 1/4 of these birds have become extinct due to their natural biological reasons.

Birds are highly organized vertebrates, whose body is covered with feathers and their forelimbs are turned into wings. The ability to move in the air, warm-bloodedness, and other features of the structure and activity gave them the opportunity to spread widely on Earth. Species of birds in tropical forests are especially diverse. In total there are about 9000 species.

This is a highly specialized and widespread class of higher vertebrates, which is a progressive branch of reptiles adapted to flight.

The similarity of birds with reptiles is evidenced by common signs:

  1) thin, poor in glands skin;
  2) strong development on the body of horn formations;
  3) the presence of cesspools, etc.

The progressive features that distinguish them from reptiles include:

  a) a higher level of development of the central nervous system, which determines the adaptive behavior of birds;
  b) high (41-42 degrees) and constant body temperature, supported by a complex system of thermoregulation;
  c) perfect reproductive organs (nest-building, hatching eggs and feeding chicks).

The evolution of birds followed a single path associated with the development of the air environment. Flying as the main way of their movement left an imprint on their external and internal structure (although they also retained the ability to move through trees, on the ground).

1) Their body is divided into a head, neck, trunk and tail. On a small head are various senses. The jaws are devoid of teeth and dressed in horn covers that form the beak. The shape of the beak is different, which is associated with the nature of the food consumed. The neck of different birds of different lengths and is highly mobile. The body has a rounded shape. The forelimbs are turned into wings. Hind - legs - of different structures. This is due to the diversity of habitats. On the legs are 4 fingers ending in claws. The lower part of the legs is covered with horny shields. The shortened tail is equipped with a fan of steering feathers. Different birds have a different structure.

2) The skin is dry, devoid of glands (except coccygeal), which is used to lubricate the feather cover and make it waterproof. The body is covered with feathers. The basis is contouring (they consist of a rod, a hearth, a fan) - they give the bird's body a streamlined shape. On the wings, they are called flyworms, and forming the plane of the tail - steering. Feathers are located under the contour with a thin rod. They lack beards of the 2nd order and, accordingly, do not form a closed fan. There is also fluff itself, which has a shortened shaft with a bunch of first-order barbs extending from them. The feather cover helps maintain a constant body temperature of birds.

3) The skeleton of birds in connection with adaptation to flight is light and durable. Lightness is due to pneumatics, and strength is due to the fusion of individual bones at an early age (skull, trunk, spine, foregut, hand bones, etc.) Tubular bones are hollow, contain air, so they are light. There are 6 sections in the skeleton: skull, spine, belt of the forelimbs, skeleton of the forelimb, belt of the hind limbs, skeleton of the hind limb. The skull is characterized by large sizes of the brain box and orbits, toothless jaws. The thin bones of the skull fuse without forming sutures. 1 condyle is used to articulate the skull with the spine. The spine consists of the cervical, thoracic, lumbar, sacral and caudal regions. Only the cervical region is mobile, all the rest are inactive or fused together (the final caudal regions are fused to the coccygeal bone). There is a chest formed by the thoracic vertebrae, outgoing ribs and sternum. In flying birds and penguins, the sternum carries a high crest - the keel, to which strong muscles are attached, providing movement of the wings (or fins). The shoulder girdle consists of a scapula, a poracoid and a clavicle - it creates a support for the wings. The pelvic girdle consists of 3 paired bones: the iliac, sciatic and pubic. Below the pelvic bones are not connected, which is associated with the laying of large eggs.

4) Musculature is important in movement both in air and on land. The muscles of the chest, raising and lowering the wing, achieve great development. In birds that have lost the ability to fly, the muscles of the hind limbs (ostriches, chickens, geese) are well developed.

5) The structure of the digestive system is characterized by further complication and is closely related to the flight of birds. They have no teeth, they are partially replaced by the sharp edges of the beak. The oral cavity is small and leads to the pharynx, which passes into the esophagus. In some, it forms an extension - goiter (in granivorous animals). Here the food is stored and softened. The stomach consists of 2 sections: the front - glandular and posterior - muscular. In the 1st chemical processing of food takes place, and in the muscular - mechanical. The intestines are short, there are blind outgrowths at the border of the thin and thick sections. The small colon does not accumulate feces, and stools are removed from the intestines very often, which facilitates the mass of the bird. The process of digesting food in birds is very active; in insectivores it does not exceed 1 hour, and in carnivores - 4 hours. Intensive metabolism is associated with the consumption of a significant amount of feed, especially increasing in small birds, which are characterized by large heat losses.

6) The respiratory system has a number of features associated with adaptation to flight. It begins with the nostrils located at the base of the beak. From the mouth, the laryngeal fissure leads into the larynx, and from it into the trachea. In the lower part of the trachea and the initial sections of the bronchi is the vocal apparatus - the lower larynx. The source of sounds are the membranes vibrating during the passage of air between the last cartilaginous rings of the trachea and the semicircles of the bronchi. The bronchi penetrate into the lungs, branch into small tubes - bronchioles - and very thin air capillaries, which form an airway network in the lungs. Blood vessels are closely intertwined with it, gas exchange occurs through the walls of the capillaries. Part of the bronchial branches is not divided into bronchioles, extends beyond the lungs, forming thin-walled air sacs located between the internal organs, muscles and even inside the hollow bones. The volume of air bags is almost 10 times the volume of the lungs. Paired lungs are small and slightly extensible, they grow to the ribs on the sides of the spine. In a calm state and while moving on the ground, the act of breathing is carried out due to the movement of the chest. The chest bone when inhaling falls, moving away from the spine, and when you exhale it rises, approaching it. During the flight, the sternum is motionless. When the wings are lifted, exhalation occurs, O2-rich air enters from the air sacs into the lungs, where gas is exchanged. Thus, air saturated with O2 passes through the lungs 2 times: both when exhaling and when inhaling (the so-called double breathing). Air bags prevent overheating of the body, as excess heat is removed with air.

7) the circulatory system of birds is represented by a 4-chamber heart (2 atria, 2 ventricles) and outgoing blood vessels. Venous blood is concentrated on the right side of the heart, and arterial blood on the left. Organs and tissues receive pure arterial blood, which contributes to enhanced metabolism and provides a constant high body temperature (38-42 degrees). From the left ventricle, arterial blood enters the right aortic arch (only in birds). Arteries that feed oxygen to all parts of the body depart from it. Venous blood through the anterior and posterior vena cava returns to the right atrium. This blood movement makes up a large circle of blood circulation. For small venous blood through the pulmonary artery comes from the right ventricle to the lungs. Oxidized blood from the lungs is sent through the pulmonary veins in the left atrium, in which the small circle ends. It circulates blood at a high speed, which is associated with the energetic work of the heart. The pulse of passerines at rest is 400-600 beats, during flight - 1000.

RIGHT ATRIUM		LEFT ATRIAL
RIGHT VENTRICLE		LEFT VENTRICLE
	LUNGS
	BIG CIRCLE BLOOD VESSELS

  8) The excretory organs are represented by 2 large kidneys lying in the depths of the pelvis. Their mass is 1-2% of body weight. Through two ureters, uric acid flows into the cloaca and is excreted along with excrement. There is no bladder, which facilitates the weight of the bird.

9) Birds are warm-blooded animals, they have a constant body temperature (an average of 42 degrees). Warm-bloodedness is due to an increase in metabolic rate by intensifying digestion, respiration, blood circulation, excretion, and the presence of heat-insulating integuments. The constancy of ambient temperature is an important progressive sign of birds in comparison with previous classes of animals.

10) The nervous system of birds in comparison with the nervous system of reptiles has become much more complicated, which is reflected in their more complex behavior. It is represented by the brain, spinal cord and departing nerves. The brain is enclosed in a volumetric brain box. The large hemispheres of the forebrain are large in size and are formed by striped bodies. The midbrain has developed visual lobes. The cerebellum ensures balance and precise coordination of the bird during the flight. The olfactory lobes are poorly developed. Cranial nerves 12 pairs.

11) The most important sensory organs are the organs of vision and hearing. Their eyes are large, equipped with upper and lower eyelids and a third century, or a blinking membrane. All birds have color vision. Visual acuity is several times higher than in humans. The organ of hearing, as in reptiles, is represented by the inner and middle ear. In the internal, the cochlea is better developed; the number of sensitive cells is increased in it. The cavity of the middle ear is large - the only auditory ossicle is a stapes of a more complex shape. The eardrum is deeper than the surface of the skin; a canal leads to it - the external auditory canal. The hearing is very sharp. Compared with reptiles in birds, the surface of the nasal cavity and olfactory epithelium is increased. In some birds (ducks, waders, carrion predators, etc.), the sense of smell is well developed and is used when searching for food. Other birds are poorly developed. The taste organs are represented by taste buds in the mucous membrane of the oral cavity, on the tongue and at its base. Many birds distinguish between salty, sweet and bitter.

12) Birds are dioecious, their fertilization is internal. In the female, only the left ovary and left oviduct function, the right ovary and oviduct are reduced. This is due to the large size of the eggs: if there were 2 ovaries, their large mass and rigid shell would make it difficult for the eggs to fly and move along the oviduct. In males the testes are paired, their ducts open in the cloaca. The eggs of birds are large due to the content of a large amount of nutrients in them. Actually the egg (or egg) of birds is called yolk. On its surface there is an embryonic disk from which the embryo develops. The bulk of the yolk serves as a supply of nutrients and water. Passing through the oviduct, the egg is first surrounded by a layer of protein, which protects it from mechanical damage and serves as a source of water for the development of the embryo, then dresses in the shell-shell and, finally, a durable calcareous shell. The shell is penetrated by the smallest pores, providing gas exchange of the embryo with the external environment. The overshell shell protects the egg from bacteria. When the egg enters the oviduct, the development of the embryo in it is only beginning. To continue development outside the body, it is necessary that the egg is heated. The birds developed an instinct for incubation, during which embryonic development takes place in the egg. At the earliest stages of development, the embryo of birds has a great resemblance to the embryos of its ancestors - a chord, gill slits and branchial arteries are laid, a long tail appears - evidence that the distant ancestors of birds were aquatic animals. Paleontological findings suggest that the immediate ancestors of the birds were reptiles.

13) According to the degree of physiological maturity of the chicks at the time of hatching, all birds are divided into 2 groups - broods and chicks. In brood chicks, immediately after hatching, they are covered with down, sighted, can move and find food. Adult birds protect their brood, periodically warm their chicks (especially in the first days of life), and help in the search for food. This includes all chicken-like (black grouse, hazel grouse, partridge, pheasant, etc.), anseriformes (geese, ducks, swans, eagles), cranes, bustards, ostriches. In chicks, chicks are initially blind, deaf, naked or slightly pubescent, cannot move, remain in the nest for a long time (in passerines - 10-12 days, in some - up to 2 months). At this time, the parents from the heat and feed. This includes pigeons, parrots, passerines, woodpeckers, and many others. Chicks leave the nest feathered, almost reaching the size of adult birds, but with uncertain flight - 1-2 weeks after departure, parents continue to feed and teach how to find food. Due to various forms of care for offspring, the fecundity of birds is much lower than that of reptiles, fish, and amphibians.

Findings:

  1. Fitness for flight in the external structure (streamlined body shape. Feather cover, wings, tail of tail feathers).
  2. The skeleton of birds is characterized by strength and lightness. These qualities are due to the fact that many bones are fused together and form strong sections (skull, trunk section of the spine, foregrip, hand bones, etc.), and the tubular bones are hollow, contain air, so they are light.
  3. Features of the muscles of birds associated with flight - a strong development of the muscles that move the wings: large pectoral muscles lower the wing, subclavian lift. Intercostal - are of great importance in the respiration of birds. Strongly developed leg muscles.
  4. Fitness for flight in the digestive system (beak without teeth, fast digestion, frequent bowel movements, etc.).
  5. Adaptability to flight in the respiratory system (air sacs help to increase the volume of inhaled air, participate in the mechanism of double breathing, promote heat transfer, protecting the body from overheating, and lighten the body weight of the bird).
  6. Features of the circulatory system (large sizes of the heart, the presence of 4 chambers, thanks to which body tissues receive arterial blood rich in oxygen). The vital processes proceed quickly (oxidation), providing an intensive metabolism and a high constant body temperature.
7. In connection with flight and a diverse lifestyle, the nervous system, in particular the brain, has a more complex structure. This is expressed in the larger sizes of its anterior section and cerebellum, in the presence of relatively large visual lobes, which is associated with a more complex structure of the organs of vision.
  8. The high development of the central nervous system is due to the more complex behavior of birds. It manifests itself in various forms of care for the offspring (nest building, laying and incubation of eggs, heating of chicks, feeding them), in seasonal movements, in the development of sound signaling. Complex forms of care for offspring in birds are progressive features that have developed in the process of their historical development.
  9. Flight adaptability in the reproductive organs (females have one left ovary and one left oviduct). Propagate on land with the help of relatively large eggs, rich in yolk and covered with a number of shells; for the development of the embryo in the egg, nutrients, oxygen and heat are needed; similarities in the reproduction and development of birds and reptiles testify to the relationship of vertebrates of these classes.

General characteristics of the class. Birds - the firstin the evolutionary series warm-blooded (homoyothermal)animals. Their body temperature is constant and relatively independent of ambient temperature. Another feature of this class is that it forms a special branch of evolution, the representatives of which acquired ability to fly.Most birds are flying species. The noted features allowed the birds to master the terrestrial, air and (partially) aquatic habitats, settle in almost all climatic zones and even change them, migrating as necessary to more favorable living conditions (migratory and nomadic species - see below).

Significant anatomical and physiological changes occurred in the body of birds in comparison with their evolutionary predecessors - reptiles. At the same time, being the “direct descendants” of reptiles, the birds preserved many of their characteristics: the absence of skin glands, the presence of horn formations in the integument (shields on legs, horn cover of the beak, claws), similar structure of excretory and reproductive systems (however, note that unlike female reptile females, female birds have solitary ovaryand oviduct- left),almost the same egg structure and development of the embryo.

Maintaining a constant body temperature of birds and a new mode of movement required an increase in the level of metabolic processes, primarily due to the high intensity of all physiological functions: digestion, respiration, blood circulation, and excretion. Food in the gastrointestinal tract of birds is digested very quickly due to the effectiveness of digestive enzymes, and after cleavage, nutrients are actively absorbed by increasing the intestinal absorption surface: the intestinal mucosa forms numerous villi.Due to the lack of teeth, the powerful function of grinding food takes on muscular stomach;beak and claws (in birds of prey) can participate in the primary mechanical processing of food. Undigested food remains do not linger in the rectum (this greatly facilitates body weight) and are removed through cesspool.Intense gas exchange in the lungs is achieved by "double breath"in which atmospheric air enters the lungs not only during inspiration, but also exhale. This is made possible through the participation of special inhalation air bags(Fig. III.31). Productive gas exchange in tissues is ensured by the fact that arterial blood enriched with oxygen comes to them. Arterial and venous blood in birds does not mix, as their heart four-chamber:solid interventricular septumcompletely divides the venous and arterial blood of the right and left ventricles. The large circle of blood circulation (see Fig. III.34, D) begins from the left ventricle with one vessel - right aortic arch.Arterial blood is distributed to all organs along the arteries extending from the aortic arch. The small circle begins from the right ventricle with a pulmonary artery carrying venous blood to the lungs, where it gives off carbon dioxide and is saturated with oxygen. Birds are characterized by a high heart rate and, therefore, a high blood flow velocity. The main end product of metabolism in most birds - uric acid - is excreted from the body through the trunk kidneys in the form of crystals (one of the ways to save fluid in the body). The bladder as an accumulative organ in birds is absent (relief of body weight).

Birds, unlike other animals, have feather cover (plumage).Feathers are horn formations of complex structure that cover the skin. By their origin, they are derivatives of reptile scales. The main role of the feather cover is associated with thermoregulation: it prevents heat dissipation from the surface of the body. The feather cover is equally important for flight. Feathers give the body a streamlined shape; the flight properties of the wings and tail largely depend on them. Feathers are diverse in their purpose and structure. Those that define the contours of the body are called, respectively. contour.They give the body a streamlined shape, which is very important for flight. Located under the contour downyfeathers and fluffprovide thermal insulation. The flight properties of the wing are associated with two rows of large flyfeathers and upper and lower covertsfeathers of a wing. Tail feathers are called steering.The pen consists of rodwhose lower end (very)immersed in the skin. Special muscles are attached to it, raising and lowering the feather. From the rod in both directions depart first-order beardswhich are located second-order beardswith hooks. Clinging to each other, the barbs form fanpen. In down feathers and down, second-order barbs are absent; the core of real fluff is greatly shortened.

The development of the structure of the musculoskeletal system: axial skeleton, skeleton of the skull and paired limbs contributed to the development of the air environment by birds. The total weight of the skeleton in birds is facilitated by the presence of air cavities in many bones. The skull is formed by thin fused bones. Jaws turned into beak:upper jaw - the beaklower - mandible.Lack of teeth also greatly facilitates the weight of the skull. In the axial skeleton, almost all vertebrae are fused; the cervical vertebrae and part of the caudal vertebrae remain mobile. The coalescence of the axial skeleton is very important, because to give the body stability on land and in the air, birds need a "rigid load-bearing structure." The sternum has an outgrowth (keel) -the place of attachment of the powerful pectoral muscles, which move the wings during flight. When moving on the ground, birds rely only on their hind limbs, and in flight use modified forelimbs - wings. Strong attachment of the hind limbs to the spine is achieved through education complex sacrum.It includes bones of the pelvic girdle, vertebrae of the sacral and lumbar regions, part of the vertebrae of the caudal region and the last thoracic vertebra. In the skeleton of both pairs of limbs, the number of fingers decreases, the bones of the wrist and metacarpus lengthen and merge (formed buckle),tarsus and metatarsus (with formation tsevki).

In the brain, the largest division is the forebrain (see Fig. III.35, D). It consists of two hemispheres with a smooth surface. The olfactory lobes of the forebrain occupy a smaller volume compared to reptiles, which indicates an insignificant role of olfaction in the life of birds. The leading organ of senses is the organ of vision; development of the optic tubercles is associated with this; primary visual information enters the well-developed visual lobes of the midbrain. The cerebellum reaches a significant size - the center of regulation and coordination of movements. Elements of higher nervous activity (in particular, memory, learning, rational activity), as well as complex forms of bird behavior (nest building, care for offspring, migration, etc.) are associated with progressive brain development.

In addition to vision, the birds have well-developed hearing, a sense of balance, muscle sensitivity. The eyes are large. The retina has a high density of photoreceptors, which allows you to get a detailed image of the object, including in flight. Many birds have color vision. The accommodation of the eye is carried out by changing the shape of the lens with its simultaneous movement relative to the retina. The organ of hearing includes three sections: the inner ear, middle ear and rudiments the outer ear.Birds are characterized by a subtle distinction of sounds in a wide range of frequencies, sound communication in their life plays one of the main roles (danger signals, marking the boundaries of the territory, attracting a marriage partner, etc.). The organ of equilibrium is vestibular apparatus.Together with muscle receptors, he participates in coordination of movements, especially important during flight.

Origin of birds. Bird ancestors - dinosaur dinosaurs- reptiles from the group of archosaurs (see Fig. III.30). For a long time the only fossil animal was known, which in appearance remotely resembled modern birds, - archeopteryx.In the Jurassic deposits of Germany, archaeologists have found 5 prints of this "first bird". Archeopteryx combined the signs of both reptiles (the presence of teeth, a long tail of 20 vertebrae, free fingers in the forelimb, lack of a keel) and birds (feather cover, the characteristic structure of the shoulder girdle and hind limb). Currently, Archeopteryx is not considered a direct ancestor of birds. He represented a parallel line of development, which developed adaptations to flight. There is still no consensus on how reptiles "learned to fly." According to one version, the ancestors of the birds led an arboreal lifestyle and gradually moved from jumping from branch to branch to planning, and then to flapping flight. According to another hypothesis, they, like many reptiles, moved on the ground only on their hind limbs. Lengthening the scales on the forelimbs allowed them to "flip" during fast running, and then move on to flapping flight.

Bird class system. Modern birds are represented by three superorders: Keyless, Penguinsand Keel.TO beskilevyminclude African and South American ostriches, as well as cassowary and kiwi. All of them are deprived of the ability to fly, wings are poorly developed, the keel is absent on the sternum; move exclusively on the ground on the hind limbs, which have highly developed muscles. Distinctive feature penguinswhich also do not fly - the ability to swim and dive. In water, they move with the help of wings, rather than hind limbs, like other floating birds. Penguins are common in the southern hemisphere. Most modern birds belong to the superorder keel.We will consider their anatomical and physiological features on one of the representatives - the gray pigeon, belonging to the order Pigeon-shaped.

Gray pigeon. Doves live in forests (clintukh, vyakhir, Streptopelia) and mountains (rocky dove). These are granivorous birds. The homeland of the gray pigeons is the foothills, but they have adapted to close proximity with humans and currently inhabit many cities, using attics and niches of stone buildings for nesting. Abundant top dressing makes the number of this species in cities very high.

A small rounded head of a gray dove ends beakconsisting of bibsand mandibles.The beak is covered with a horn cover. At the base of the beak there are openings of the nostrils, an area of \u200b\u200bsoft bare skin adjoins them - waxen.On the sides of the head are large eyes, protected by the upper and lower eyelids and blinking membrane.Behind the eyes are external auditory openings,tightened by the eardrum and covered with feathers. The neck is relatively long and mobile. At a pigeon standing on the ground, the thigh and lower leg are hidden by plumage and only the tarsus, covered with horn scales, is visible. Four fingers end with claws.

The body of the dove is covered with feathers. The upper feathers are contour. Below them are down feathers and real down, providing thermal insulation. Areas covered with contour feathers alternate with areas of bare skin. By giving away excess heat, the non-feathered areas protect the body from overheating. The wing plane is formed by two rows of large fly feathers, partially covered by the upper and lower covering feathers of the wing. Tail feathers perform the function corresponding to the name.

Leatherthe pigeon is thin and dry. The only cutaneous gland located at the base of the tail (coccygeal),gives off a greasy secretion for greasing feathers. This gives them elasticity and water-repellent properties.

AT the spinepigeons are distinguished by cervical, thoracic, lumbar, sacral and caudal, but in connection with adaptation to flight, they underwent significant changes.

The pigeon's skull is large (relative to the body), which is associated with an increase in the size of the brain located in it. The bones of the skull are thin and fuse without seams. Large eye sockets create conditions for eye mobility. The jaw is represented by a beak covered with a horn cover and devoid of teeth.

Forelimb Beltdove, turned into wings, includes saber-shaped shoulder blades, directed down powerful coracoids (crow bones) and clavicles fused to little fork.The sternum is connected to the spine by ribs. From the lower surface of the sternum outgrowth - keel(hence the name of the superorder) - the place of attachment of powerful "flying" muscles. Free forelimbconsists of a shoulder, forearm and hand, elongated due to the formation of a buckle. Of the five fingers, three remain, with a reduced number of phalanges (Fig. III.32).

Pelvic girdleopen, i.e., its left and right halves do not fuse on the ventral side; this allows females to lay relatively large eggs. In the skeleton free hind limbin addition to the thigh and lower leg, there is a third link - the tarsus. In the skeleton of the tibia, the fibula is greatly reduced in size and grows to the tibia. The hind limb of the pigeon has four fingers with claws: three of them are directed forward, one is back. This arrangement creates a reliable support and fixation on any surface (Fig. III.33).

Musculaturethe pigeon is divided into the muscles of the head, neck, trunk and limbs. Long neck muscles provide complex head movements. Most of the muscles of the body are involved in flight, raising and lowering the wings - this subclavianand large pectoralmuscles that attach to the sternum and to the keel. Strongly developed muscles of the hind limbs, intended only for movement on the ground.

Features digestionassociated with the need to intensify the processes of life. The process of digesting food in a pigeon, like all birds, is accelerated. The stomach is divided into two sections: glandularand muscular.In the glandular stomach, food is digested (chemically processed) by enzymes secreted by numerous digestive glands. The mechanical processing of food (grinding of grain) occurs due to contractions of the powerful muscles of the walls of the second section of the stomach - the muscular one. Its inner surface has a dense horn lining and is devoid of glands. To grind food more efficiently, pigeons, like many other herbivorous birds, swallow small stones that linger in the stomach and act as millstones. The stomach cavity is small, and it cannot play the role of a food store. This function goes to a special expansion of the esophagus - goiter.It also performs another function: in the first days after hatching, the pigeons feed them with the so-called "goiter milk"formed as a result of desquamation of epithelial cells of the goiter lining. In the anterior part of the small intestine - the duodenum - the ducts of the pancreas and liver open. At the border of the small and large intestines are paired cecum. The rectum is very short, undigested food debris does not accumulate in it and is quickly excreted through the cloaca.

Process breathingthe pigeon is very intense (providing thermoregulation and flying function). Air enters through the nostrils into the oral cavity, and from there into the larynx and the long trachea, which is divided into two bronchi. In the place of separation of the trachea, thin membranes are stretched - vocal cords.Due to the fluctuation of the membranes caused by the flow of air, pigeons, like other birds, make a variety of sounds. In the lungs, they move away from the bronchi secondary bronchiand from them - parabronchi.This determines the spongy structure of the lungs of a pigeon that is practically incapable of expansion. Thin-walled air is used to pump air into the lungs and expel it. air bags.They are located between all internal organs, and some even enter the tubular bones of the forelimbs. Expanding and contracting when lowering and raising the sternum, the bags pump air through the lungs (see Fig. III.31). When inhaling, most of the air flows through the bronchus into the posterior air sacs, a smaller portion gets into the lungs. When you exhale, air from the rear sacs is sent to the lungs, from them to the front air sacs, from where it is released through the trachea. Thus, atmospheric air enters the lungs and when you inhaleand when exhaling (double breathing).

The pigeon’s heart has four chambers: the ventricles are completely separated by a vertical septum. The resting heart rate is very high: 200-300 beats per minute, and during flight reaches up to 500 beats per minute. The pulmonary circulation begins with a pulmonary artery that carries blood from the right ventricle to the lungs. Blood enriched with oxygen from the lungs enters the paired pulmonary veins into the left atrium. The remaining vessels belong to a large circle of blood circulation. The only right aortic arch carries arterial blood from the left ventricle. Paired vessels (from one trunk) to the head (carotid arteries) and very large arteries supplying the forelimbs and powerful pectoral muscles with blood depart from it. Turning to the dorsal side, the right arch passes into the dorsal aorta, giving the vessels to all organs. From organs located in the front of the body, blood is collected in paired anterior vena cava. Veins that carry blood from all other organs merge into the posterior vena cava. Two anterior and one posterior vena cava flow into the right atrium. From it, venous blood enters the right ventricle and from there into the pulmonary circulation (see Fig. III.34, D).

For brainthe pigeon, like other birds, is characterized by an increase in the size of the forebrain hemispheres. Their surface, covered with a layer of gray matter, has no furrows and convolutions. The olfactory lobes occupy a small volume, the visual lobes of the midbrain are developed. The large cerebellum adjoins the hemispheres of the forebrain, covering the midbrain and a large part of the medulla oblongata (Fig. III.35, D).

Leading sensory organspigeons - organs of vision and hearing. Large eyes are protected by moving eyelids and a blinking membrane. The accommodation of the eye is carried out both by changing the shape of the lens, and by its simultaneous movement relative to the retina. The retina has a high density of photoreceptors. The ear includes three sections: the inner ear, middle ear and the rudiments of the outer ear.

Organs selection -pelvic kidneys - consist of three lobes. The kidneys are located on the dorsal side of the body and fit snugly against the bones of the complex sacrum. From the kidneys the ureters flow into the cloaca; the bladder is absent. Uric acid, the final metabolic product, is excreted from the cloaca along with droppings.

Organs breedingmales are represented by paired testes, from which the vas deferens, flowing into the cloaca, depart; females have a single, left, ovary. A mature egg gets from the ovary into the oviduct and, moving along it into the cloaca, dresses protein, subshelland shell shells.The substances that form these membranes are secreted by the glands of the walls of the oviduct. Fertilization is internal: it occurs in the upper parts of the oviduct, since the sperm must merge with the egg before the formation of dense egg shells.

A female pigeon lays 2 eggs in a nest built of small twigs and devoid of a special lining. During incubation, which lasts 16-19 days, the nest maintains temperature and humidity, optimal for the development of the embryo. Development occurs due to the large amount of nutrients contained in the yolk of the egg. Hatching pigeon chicks are naked, blind and completely dependent on their parents (they need heating and frequent feeding). In the first days of life, pigeons feed their chicks with “goiter milk” (see above), then they belch out partially digested food. Almost full-fledged chicks leaving the nests (nests) are switching to grain nutrition.

Features of reproduction and development of birds. The breeding season in most birds begins with the onset of spring. An increase in the length of daylight stimulates the production of germ cells by the ovaries and testes of birds; an increase in air temperature, along with other factors, determines the beginning of the construction of nests. The egg-laying time is associated with natural conditions (mainly the availability and abundance of food), not only at the time of its beginning, but also throughout the entire period of hatching and feeding of the chicks.

Most birds stay during breeding in pairs. Some of them change their partner every year (small passerines), in other species the pairs remain for several years, and sometimes even throughout their lives (geese, large birds of prey, herons, storks). For nesting, pairs, as a rule, occupy areas that vary greatly in size in birds of different species, and protect them from competitors. Attachment to certain breeding sites is due to the presence of optimal breeding conditions. Some birds nest in colonies (crested cormorants, some gulls).

The methods for constructing the nest, the types of building materials, and the location of the nests are very diverse among class representatives. Some species arrange nests on the ground (geese, many ducks, larks, wagtails, etc.), laying their eggs in small cavities in the ground (many waders) or on stones (scallops) without litter. Birds can nest on tree branches (rooks, thrushes, many other passerines), in hollows (tits, woodpeckers, flytraps, owls, gogol, etc.), on rocks (scallops, seagulls, birds of prey) and in burrows ( shore swallows, bluefin, kingfisher, cinder). Toadstools arrange floating nests of grass and reeds. Nests of some birds are heaps of grass (gulls, loons) or twigs (pigeons, crows, herons, birds of prey). Most small passerines build nests in the form of a bowl using a wide variety of materials: fresh and dry grass, twigs, leaves, feathers, wool, clay, etc. Weavers and some other birds make complex nests in the form of bags with entrances, corridors, sometimes with lids, and hang them on branches. Both partners (pigeons, gulls), only a female (tits, nightingales, nuthatching) or only male (warblers, wrens, many weavers) can take part in the construction of the nest. The laid eggs - the clutch - are incubated either by one of the parents (in most passerines, owls, geese, gulls and birds of prey - only a female, in many waders, kiwi, nandu and cassowary - only male), or both alternately. Weed chickens living in Australia do not hatch eggs at all. They bury them in sand or piles of decaying leaves and, periodically raking or filling up these piles, maintain the optimum temperature for embryo development in them.

In some birds (passerines, woodpeckers, cuckoos, swifts, pigeons, etc.) almost completely naked blind chicks with weak limbs and poorly developed sense organs hatch from eggs; they need not only feeding, but also heating and protection from overheating. These species are called chicks.In birds of other species, chicks are able to independently move and feed within a few hours after hatching. They have relatively strong legs, their body is covered with thick down, their sense organs are well developed. Such chicks leave the nest soon after hatching and never return to it again. The role of parents in this case is to bring the chicks to places with the most abundant and affordable food for them, protect them from predators and warn of danger. Birds with this type of development nest mainly on the ground and are called brood.These include chicken, plate-billed (geese, ducks and swans), cranes, bustards, loons, waders. Chicks of gulls, goats, owls and daytime predators hatch in a dense downy outfit, they can move around, but are not able to get food themselves.

Only weed chickens can fly on the first day of life. Chicks of all other species are capable of flying only after their downy outfit is replaced by feathers. For most passerines, this occurs one and a half to three weeks after hatching, for falcons - after one and a half, and for geese - after two months. For some time, the nestling chicks are still not able to feed on their own, so parents continue to feed them.

Some young birds lead a solitary lifestyle (predators), others keep broods until next spring (finches, tits, nuthatching). Chicks of swans and many geese can keep in touch with their parents until the next breeding season, flying away with them for the winter and returning to the nesting sites.

Seasonal phenomena in the life of birds. All birds can be divided into migratory, wanderingand sedentary.TO migratorythese include species that annually leave nesting areas and fly away to specific wintering sites, sometimes over significant distances. Many birds flying from Europe to Africa in winter must fly about 9-10 thousand km one way. Approximately the same distance must be covered by birds migrating from the north-eastern regions of Russia to Western Europe (for example, turukhtanam). The farthest journey is made by polar terns, flying about 17.5 thousand km from nesting sites (in the Arctic) to wintering areas (in Antarctica, i.e. at the other extreme of the globe). Nomadicbirds (bullfinches, waxwings, woodpeckers, tits) do not make regular flights in strictly defined directions. Their wintering place is the area closest to the nesting site with the most optimal conditions for the winter season. Birds wintering in the same places where they breed are called settled.These include sparrows, capercaillie, black grouse. Some birds of the same species, living in different regions, can be both migratory and settled. For example, peregrine falcons of the northern tundra are migratory, those living in the middle lane make only seasonal migrations, and Caucasian and Crimean peregrine falcons lead a sedentary lifestyle.