Birds (scientific name: birds) are animals of Chordata in the animal kingdom. There are many kinds in the world. The bird's body is streamlined (spindle-shaped or spindle-shaped) and its surface is covered with feathers. Generally, forelimbs become wings (some kinds of wings degenerate).
Short rectum and developed digestive system help to lose weight. The heart has two atria and two ventricles, and its heartbeat is fast. In addition to the lungs, the respiratory organs also have multiple airbags to assist breathing, so that birds have oxygen passing through the lungs when inhaling and exhaling, that is, double breathing.
Birds are higher vertebrates that adapt to life on land and in the air. Long feathers can keep the body warm; There are protruding keel processes on the chest, and there are many gaps in the whole body bones, which are full of qi, so they are light; The forelegs become wings, and the hind legs walk. Most of them can fly and have a wide range of activities. Some of them can't fly because of the degradation of wings, and the activity area is relatively small, such as ostriches, penguins and most poultry.
Horny beak, toothless, some birds have migration behavior. Greatly improved the survival rate of chicks. Birds can build nests, hatch eggs, brood and migrate. There are many kinds and quantities with traces all over the world. Some birds live and breed in their breeding areas all the year round and do not migrate because of seasonal changes, which is called "resident birds"; Some birds migrate from south to north every spring and from north to south in late autumn. This kind of bird is called "migratory bird".
Birds are closely related to humans. Poultry can provide meat and eggs; Some beneficial birds can kill pests and rodents and protect crops and trees, such as swallows and owls. Some birds are available for viewing. In order to protect the ecological environment, we should take good care of beneficial birds and prohibit killing. The research on the origin of birds has gone through several stages.
1868, Huxley put forward the hypothesis that birds originated from dinosaurs. Huxley is a famous British biologist and a staunch supporter of Darwin's theory of evolution. At the same time, he was also the first scholar to put forward the theory that birds originated from dinosaurs.