You can often hear the question: are birds animals or not? Having studied all the features of the structure and life of representatives of this class, it will be possible to answer it with confidence.
General Features
The Bird class includes 9000 species united in the following superorders: keelless, or running (ostriches, kiwi), penguins, or swimming (emperor penguin, spectacled, Magellanic, Galapagos, crested and others), keeled, or flying (chicken, pigeon, sparrow, goose and others).
Birds are similar in structure to reptiles and represent a progressive branch that was able to adapt to flight. Their forelimbs evolved into wings during evolution. Birds are characterized by a constant body temperature, characteristic of higher vertebrates, therefore, birds are warm-blooded animals. This is the first answer to the question "Is a bird an animal or not?".
Birds owe their origin to the most ancient reptile pseudosuchians with a similar structure of the hind limbs.
Body and skin
The body of birds has a streamlined shape with a small head and a long movable neck. The body ends with a tail.
Leatherthin, dry, practically devoid of glands. Only a few birds (waterfowl) have an oil gland that produces a fat-like secret with water-repellent properties. Horn formations (derivatives of the epidermis of the skin) cover the beak, claws, scales of the fingers and the tarsus (lower part of the lower leg). Feathers are also derivatives of leather. They are divided into two groups: contour and down. Contour, in turn, are steering (flight control), flywheel (keeping the bird in the air), as well as coverts (located on top of the body). Under the contour are down feathers. They help retain body heat. During the molting process, older feathers fall out completely, and new ones grow in their place.
Skeleton and muscular system
In birds, the skeleton is especially strong and light due to the cavities in the bones filled with air. It consists of the following sections: cervical and thoracic, lumbar and sacral, as well as caudal. The cervical region is extremely mobile due to the many vertebrae. In the thoracic region, the vertebrae are tightly fused and bear ribs, movably connected to the sternum and forming the chest. To attach the muscles that set the wings in motion, there is a protrusion on the sternum - the keel. As a result of the fusion of the lumbar and sacral, as well as partially caudal vertebrae between themselves and with the pelvic bones, a sacrum is formed, which serves as a support for the hind limbs.
The muscular system of birds is well developed. Depending on the ability to fly, certain departments achieve special development. At the birdsthose who fly well, the muscles that set the wing in motion are well developed, and those who have lost this ability have the muscles of the hind limbs and neck.
Digestive and excretory systems
The digestive system is characterized by the absence of teeth. To capture and hold food, a beak with horn covers on the jaws is used. Through the mouth, food enters the pharynx, and after it - into the long esophagus, which has a pocket-like extension (goiter) to soften it. The posterior end of the esophagus opens into the stomach, which is divided into two sections, glandular and muscular (here the food undergoes mechanical grinding). The intestine consists of the duodenum, where the liver ducts open, and the pancreas, as well as the small and short rectum, ending in the cloaca. This structure contributes to the rapid removal of undigested residues to the outside.
The excretory organs of birds include the paired kidneys and ureters, which open into the cloaca. Urine is excreted from it along with feces.
Respiratory system
The respiratory organs of birds are maximally adapted for flight. Through the nasal cavity, air enters the pharynx and trachea, which divides into two bronchi in the chest. Here is the voice box. Once in the lungs, the bronchi branch strongly. The lungs themselves have a complex structure and consist of numerous through tubes. Some of them expand, forming air sacs, they are located between the internal organs, muscles and in tubular bones. Birds tend to breathe twice. This happens due to the fact thatduring flight, air passes through the lungs twice: when it is sucked in on a flap of the wing and pushed out when lowered due to the compression of the bags.
Nervous system
The organization of the nervous system in birds is quite complex and similar to that of higher vertebrates. This once again gives an affirmative answer to the question "Is a bird an animal or not?" The system consists of two parts: the brain and the spinal cord. In the head section, the cerebellum is well developed, which is responsible for the coordination of movements, as well as the anterior hemispheres and the midbrain, which are responsible for complex forms of behavior. The spinal cord is most developed in the shoulder, lumbar and sacral regions, which provides good motor functions. These features also give a clear affirmative answer to the question "Is a bird an animal or not?"
The behavior of birds is based on unconditioned (innate) reflexes: feeding, reproduction, nesting, laying eggs, mating games, singing. Unlike the class of reptiles, they can form and consolidate conditioned (acquired in the process of life) reflexes, which indicates their highest stage of evolution. One example of conditioned reflexes can be the fact of their successful domestication by man. It is believed that birds are domestic animals that easily rebuild their behavior and lifestyle from the wild (natural) type to the cultural (domestic) type.
Circulatory system
The organs of the circulatory system of birds, like most higher vertebrates, are represented by a four-chambered heart,consisting of atria (2) and ventricles (2), as well as vessels. Their blood is completely divided into venous and arterial. She goes through two circles of blood circulation (small, large).
Reproduction
Birds are dioecious animals with a complex and highly developed system of mating behavior, breeding with eggs and caring for them.
All of the above characteristics of the class give an unambiguous answer to the question "Is a bird an animal or not?" Of course, birds are animals.
