The Bird class has about 9000 species. Birds are distributed throughout the globe and are adapted to a wide variety of environmental conditions.
Characteristic features of the external structure of birds
- Dry skin, without glands, covered with feathers;
- the presence of wings;
- streamlined body shape;
- special arrangement of fingers on the lower extremities and the presence of a tarsus;
- the presence of a beak;
- the emergence of a four-chambered heart, which led to a complete separation of the flows of venous and arterial blood and warm-bloodedness.
The skin of birds is thin, almost devoid of glands. There is only the coccygeal gland, the secret of which is to create the waterproofness of the feather cover. Ostriches and bustards do not have a coccygeal gland.
The horny formations of the skin are the beak, claws, horny shields of the tarsus, feathers.
Feathers are modified scales of reptiles. They are formed from the horny substance.
The basis of the plumage is made up of contour feathers, which can be coverts, flight feathers and steering feathers. Down feathers are located under the contour feathers, which serve to reduce heat transfer.
The feather consists of a quill, a shaft and a fan. The fan consists of first-order barbs (without hooks) and second-order barbs (with hooks).
The birds are molting. There are 2 or more molts per year.
The wings are modified forelimbs.
The special arrangement of the fingers on the lower limbs and the presence of a tarsus
To keep the bird on the tree branches, the birds’ fingers are positioned in a special way: three fingers forward, and one toes back.
The tarsus is the fused small bones of the foot. It serves birds for “soft landing”.
The tarsus and fingers of birds are covered with horny scales, there are claws on the fingers, which indicates the relationship of birds with reptiles.
The birds’ jaws are extended into a beak and are covered with a horny covering. In the beak, a distinction is made between the upper beak (upper part) and lower beak (lower part).
The shape and size of the beak depends on the nature of the food consumed.