often hears the question: birds - are animals or not?After reviewing all the features of the structure and activity of this class, you can confidently answer it.
Class Birds includes 9,000 species, united in following superorders: ratites, or running (ostrich, kiwi), penguins, or floating (Penguin Imperial, spectacled, Magellan, Galapagos, crested and others), pitching,or flying (chicken, pigeon, sparrow, crow, etc.).
Birds on a structure similar to the reptiles and are progressive branch, which was able to adapt to the flight.Their front limbs during evolution transformed into wings.For the birds characteristic of a constant body temperature, characteristic of higher vertebrates, thus birds - warm-blooded animals.This is the first answer to the question "Bird - an animal or not."
The origin of birds required to ancient reptiles pseudosuchian with a similar structure of the hind limbs.
Body and skin
bird's body is streamlined with a small head and long neck mobile.The body ends tail.
skin is thin, dry and almost devoid of glands.Only a few birds (waterfowl) have an oil gland produced by fat-like secret with water-repellent properties.Horny education (derived epidermis) cover the beak, claws, scales fingers and tarsus (lower part of the lower leg).Feathers are also derived from the skin.They are divided into two groups: the contour and down.Outlined in turn, are steering (flight control), Makhov (maintenance of the birds in the air) and opaque (located on top of the body).Under the contour are down feathers.They help maintain body heat.During molting older feathers fall out completely and new grow in their place.
skeleton and muscular system
Birds skeleton is particularly robust and easy due to the bone cavity filled with air.It consists of the following sections: the cervical and thoracic, lumbar, and sacral and caudal.Extremely moving is due to the cervical vertebrae of the set.The thoracic vertebrae are fused tightly and edges are slidably connected to the sternum and rib cage generators.For the attachment of muscles, resulting in movement of the wings, there is a projection on the breastbone - keel.As a result of fusion of the lumbar and sacral and caudal vertebrae in part with each other and with the pelvic bones form the sacrum, which serves the rear limbs support.
muscular system is well developed in birds.Depending on the ability to fly a particular development reaches a certain department.Birds that fly well, well developed muscles that move the wings, and those who have lost this ability - the muscles of the hind limbs and neck.
digestive and excretory systems
digestive system is characterized by the absence of teeth.For grasping and holding food used with horny beak covers on the jaws.After food enters the mouth into the throat, and after it - a long esophagus, which has a pocket-enlargement (goiter) to soften it.The rear end of the esophagus opens into the stomach, which is divided into two sections, the glandular and muscular (where food passes mechanical grinding).The intestine consists of the duodenum, which open ducts of the liver, and pancreas, as well as a thin and short rectum, ending cloaca.This structure facilitates the rapid removal of undigested residues out.
The organs allocation birds are paired kidneys and ureters, which open into the cloaca.From her urine with faeces discharged to the outside.
Respiratory birds most adapted for flight.Through the nasal cavity air enters the pharynx and trachea, chest which is divided into two bronchi.Here is the voice box.Once in the lungs, the bronchi branch out much.Lungs themselves have a complex structure and consist of multiple-through tubes.Some of them extend, forming air bags are disposed between the internal organs, muscles and in tubular bones.Birds tend to double breath.This is due to the fact that during the flight of the air passes twice through the lung: the sucking in stroke of the wing to its ejection and during lowering of the compression of the bags.
organization of the nervous system in birds is quite complex and similar to that in higher vertebrates.This once again gives an affirmative answer to the question "Bird - an animal or not?"System consists of two divisions: the brain and spinal cord.The head department of a well-developed cerebellum, responsible for the coordination of movements, as well as the front hemisphere and the average brain responsible for complex forms of behavior.The spinal cord is the most developed in the shoulder, lumbar and sacral, which provides good motor functions.These features also give a clear affirmative answer to the question "Bird - an animal or not?"
behavior of birds is based on the unconditional (congenital) reflexes: nutrition, reproduction, nesting, egg laying, courtship, singing.Unlike the class of reptiles they can be configured and secured conditional (acquired during life) reflections, indicating their higher stage of evolution.One example of conditioned reflexes may be the fact that they successfully domesticated by man.It is believed that a bird - pets that are easy to rebuild their behavior and way of life from the wild (natural) such as the cultural (home).
bodies circulatory system of birds, like most higher vertebrates, represented four-chambered heart consisting of atrial (2) and the ventricles (2), as well as vessels.Their blood is completely divided into the venous and arterial.It runs two circulation (small, large).
Breeding Birds - dioecious animals with a complex and highly developed system of mating behavior, breeding using eggs and care for it.
All of the above characteristics of the class give a definite answer to the question "Bird - an animal or not?"Of course, the birds are animals.