What is the external and internal structure of birds? How are they different from other classes of animals? What signs are characteristic only of birds? You will find answers to these questions in this article.
General characteristics of birds
Birds are a class of animals whose body is covered with feathers. They have a constant and high body temperature and are active at any time of the year. The ability to fly is characteristic of most representatives of this class. The external and internal structure of birds is subject to this feature.
Birds can easily change their place of residence depending on the conditions. Due to the ability to fly, the class is widespread, found in a wide variety of conditions throughout the planet. There are about 9,000 species of birds.
Birds also have a pronounced concern for their own offspring. Reproduction occurs with large, calcareous eggs.
The external structure of birds
The body of a bird consists of a head, a movable neck, a teardrop-shaped torso and limbs. The skin is thin and dry due to the absence of skin glands. Most birds have a gland that serves tolubrication of feathers - coccygeal. It is especially well developed in waterfowl. The secret secreted by the gland serves to maintain the elasticity of the feathers and prevents them from getting wet. In some species (ostriches, parrots, pigeons, bustards), the function of lubrication is carried out by special powdery feathers, which form a powder when broken off.
Birds may have various growths on the beak, legs, head. In some species of birds (for example, birds of prey and parrots), the base of the beak is covered with soft wax. There may be plates, fringes, membranes on the legs.
The external and internal structure of birds directly depends on the way of life. The shape of the body, head, paws and tail, wings can be very diverse. It all depends on the habitat and how food is obtained.
The external structure of birds. Plumage
Only the class of birds has a feather cover, so they are also called feathered. The plumage fits snugly to the body and gives it a streamlined shape. The cover is light and retains heat well, which helps to incubate the eggs. Some feathers, due to their structure, provide the ability to fly (tail and flight feathers).
Feathers themselves are derivatives of the skin, akin to the scales of reptiles. The structure of the feather is as follows: its trunk consists of a dense rod, ending with a chin (hollow end). Fans are attached to the rod. They consist of horny plates - beards. Barbs extend from the rod, having branches called barbs. Some of them are strewn with hooks with which they are connected.with neighboring beards without hooks. A large feather can be made up of a million beards.
This structure ensures the density of the fan. During flight, very little air can pass through the feather. If the barbs come apart, the bird will straighten them with its beak when cleaning feathers.
The functionality of feathers can be divided into two groups: down and contour. Downy feathers have a loose fan. There is also just fluff - feathers, consisting of almost only beards, with an undeveloped core. There are also bristle feathers, which, on the contrary, consist of rods, with little or no barbs. There are also hair-like feathers on which the function of touch is assigned. Contour feathers can be divided into primary, tail, covering and integumentary. Each type of pen performs its own function. The varied color of feathers is due to the presence of pigments.
Musculoskeletal system
Features of the internal structure of birds are associated with a trait inherent only in birds - the ability to fly. The skeleton of a bird is light, but at the same time it has great strength, it consists of thin hollow bones. It includes the skull, spine, limb girdles, and limb bones. The skeleton protects the internal organs.
The internal structure of birds suggests a large volume of the skull. Eye sockets are enlarged, jaws form a beak, teeth are missing. The spine is divided into 5 sections: cervical, thoracic, lumbar, sacral, caudal. The vertebrae of the cervical region have a special structure, thanks to which the bird can turn its head 180degrees.
The thoracic vertebrae fuse and form a single bone to which the ribs are attached. Flying bird species have a keel on the sternum. This is a large outgrowth on which powerful wing muscles are attached. The vertebrae of the lumbar and sacral are also fused to serve as a reliable support for the pelvis, and the caudal vertebrae are fused into a single coccygeal bone to become a support for the tail feathers.
The shoulder girdle is made up of three pairs of bones: the clavicle, shoulder blades and crow bones. The wing consists of the humerus, forearm and bones of the hand. The bones of the pelvis fuse with the vertebrae and serve as a support for the lower extremities. The leg consists of the thigh, lower leg, tarsus (several fused bones of the foot) and toes.
The muscles of the bird, located from the keel to the shoulder, ensure the work of the wings. In flying birds, the muscles in this part are especially well developed. The muscles of the neck provide the movement of the head. The internal structure of birds is interesting in the area of \u200b\u200bthe structure of the muscles and tendons of the lower extremities. Through the joints of the legs, tendons stretch, which end in the fingers. When a bird perches on a tree and bends its legs, the tendons tighten and the toes wrap around the branch. Thanks to this feature, the birds can sleep on the branches, their fingers do not open.
Digestive system
We continue to study the internal structure of birds. General characteristics begin with the first section of the digestive system - the beak. It is the bones of the jaws, covered with horny sheaths. The shape of the beak depends on the method of obtaining food. Teeth atthere are no feathers. The food is swallowed whole, from a large piece, with the help of its beak, the bird can tear off suitable pieces.
The esophagus of birds can stretch significantly. Some types of birds can fill it with food and not experience discomfort. There may be a goiter at the end of the esophagus, a special extension adapted to store food.
The stomach of a bird consists of a glandular and muscular section. In the first, the secretion of gastric juice occurs, which softens the food, and in the second, it is grinded. This process is facilitated by pebbles that are swallowed by birds. The stomach is followed by the intestine, ending in a cloaca. The ureters and excretory tracts of the reproductive organs also open in the cloaca.
Respiratory system
We continue to study the internal organs of birds. The internal structure of birds is subject to the need to ensure flight. This also applies to the respiratory system, which is represented not only by the lungs, but also by air sacs located in the free space between the internal organs. These sacs are connected to the lungs and have the important function of providing breathing during flight. At rest, the bird breathes with the lungs, working with the chest.
In flight, thanks to the work of the wings, the air sacs expand and contract, supplying air to the lungs. The faster the bird flaps its wings, the more often the air sacs contract. For example, a dove takes 26 breaths at rest, and up to 400 in flight. Thanks to active air circulation, the bird's body cools down. Oxygen-enriched air from the breathing bags enters the lungs, which does not allow the bird to suffocate.
The circulatory system of birds
Features of the internal structure of birds can also be found by studying the circulatory system, which is represented by two circles of blood circulation and a four-chambered heart. The large and small circles of blood circulation are completely separated, that is, arterial and venous blood do not mix. The heart consists of two atria and two ventricles.
The heart muscle is capable of accelerating its work dozens of times, for example, at rest, the heart of a pigeon contracts 165 times per minute, and during the flight - 550 times. The structural features of the circulatory system of birds are caused by a high level of metabolism. The heart has a large volume, the pulse is frequent, the blood is saturated with oxygen and sugars - all this ensures both an intensive supply of all organs with the necessary substances and the rapid removal of metabolic products.
Sense Organs
The organs of smell in birds are poorly developed. Most birds are unable to distinguish smells. The internal structure of birds, especially the organs of hearing, is more developed than that of reptiles. The organs of hearing are represented by the inner, middle and outer ear. The latter consists of a deep external auditory meatus framed by skin folds and special feathers.
Birds have well developed organs of vision. Eyes of large size and complex structure, good sensitivity. Color vision is better developed than in many other animals. Birds distinguish bignumber of shades. At a high speed of movement during the flight, vision allows you to assess the situation from a great distance, but the bird sees objects that are a few centimeters away clearly.
Nervous system
In flight, birds make complex movements, so the cerebellum, which is responsible for coordination, is large. The visual tubercles are also well developed. The forebrain hemispheres are enlarged. The internal structure of birds, their brain and nervous system is associated with the complex behavior of birds.
Most of the actions are instinctive - building a nest, forming pairs, caring for offspring. But with age, birds are able to learn. If the chicks do not feel fear of a person, then adults are afraid of people. They can distinguish a hunter from an unarmed one, and crows can understand what exactly is in a person’s hand - a stick or a gun.
Some species of birds recognize people who often feed them, can be trained and are able to imitate various sounds, including human speech.
Excretory and reproductive systems
Let's consider the excretory and reproductive systems, their internal structure and reproduction of birds. Since the metabolism of birds is accelerated, the kidneys are large. These paired metanephric organs are divided into three lobes and are located under the dorsal walls of the pelvis. The ureters that depart from them open in the cloaca. Birds do not have a bladder. Waste products, predominantly uric acid, are rapidly eliminated from the body.
Copulatory organmost birds are not. The testicles, which increase in size during the breeding season, discharge the contents through the canal into the seminal vesicle located in the cloaca.
The internal structure of birds, or rather, the reproductive organs of females, has interesting features. They have developed only the left ovary and oviduct, the right ones are usually rudimentary. Most likely this is due to the lack of space for the simultaneous formation of large eggs. The oviduct departs from the ovary, which is divided into several sections: a long fallopian tube, a thin-walled and wide uterus, and a narrow vagina that opens into the cloaca. To carry out fertilization, the male presses his cloaca against the cloaca of the female.
Reproduction and care of offspring
We examined the internal structure of birds. Biology not only studies anatomy, but also analyzes the behavior of animals. Let's talk about such a complex process as reproduction and care for offspring in birds.
The breeding season is when enough food is available. Our birds - in spring and summer. But reproduction in birds kept in captivity, for example decorative ones, is stimulated at any time of the year, increasing the amount and nutritional value of the feed.
Most small and medium birds form pairs for a season, large ones often have long unions. They can form flocks, where temporary pairs are formed. The choice of a partner is not accidental. Males lek to attract the attention of females: spread their feathers, make special sounds, enter into fights.
Most species lay their eggs in a nest that can be located on the ground, in trees, bushes, inhollows, minks. Eggs are protected by a strong shell, often camouflaged.
In brood species (poultry birds, ducks, geese, black grouse, swans), chicks emerge from the egg with open eyes and covered with down. Very quickly they begin to eat on their own and leave the nest. In breeding birds (pigeons, crows, tits, sparrows, rooks, parrots, birds of prey), cubs appear blind and naked, completely helpless.
Birds are characterized by long-term care for offspring. Birds keep and feed their chicks and protect them.
