A flock of birds are twittering around, courting or looking for insects to eat.

Birds singing together usually appear in three scenes: the first is that birds communicate with each other in a relatively safe environment; The second is courtship; The third is to call a partner.

Birds, also known as birds. Definition: Egg-laying vertebrates covered with feathers. The main characteristics of birds are: streamlined bodies (spindle or spindle), most of which can fly. The body surface is covered with feathers, and the forelimbs generally become wings (some kinds of wings degenerate); The pectoral muscles are developed; Short rectum, large appetite and fast digestion, that is, the digestive system is developed, which helps to lose weight; The heart has two atria and two ventricles, and its heartbeat is fast. The body temperature is constant. In addition to the lungs, the respiratory organs also have multiple airbags to assist breathing, so that birds can have oxygen passing through the lungs when inhaling and exhaling, that is, double breathing.