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Korea Biodiversity Information System > Wildlife Resource > Bird Classes > Characteristics of Birds
Their entire body is covered with feathers where there are no sweat glands, and oil from a preening gland acts as waterproofing for the feathers.
They lay and hatch eggs after entosomatic fertilization.
They are homeothermic animals with a constant body temperature.
Their bodies are largely divided into head, body, wings, and legs.
They have wings with lightweight bones (that have air-filled cavities), which make flying possible. Their chest bones and muscles are strongly developed to fly better.
They breathe using lungs, but also have air sacs directly connected to their lungs, unlike mammals.
Their feet are generally composed of four toes, usually three in the front and one in the back.
Have well developed upper and lower jaws and can cut and grind food to the proper size with specialized teeth (incisors, canine tooth, premolar and molars).
