Why do birds fly?

First, because of feathers. The feathers on the outside of birds not only keep warm, but also streamline the bird's appearance, which has little movement resistance in the air and is beneficial to flying. When the wings flap up and down to encourage airflow, it will produce great downward resistance and make the bird fly forward quickly.

The second is bone. Birds' bones are light, hollow and full of air. Moreover, the bird's skeleton structure is unique, which reduces the weight and strengthens the flying ability.

The third respiratory system. Birds have muscular breasts and a unique respiratory system to adapt to flying life. The unique double breathing ensures that birds have enough oxygen during flight.

Finally, all the organs of birds are beneficial to lose weight, but other reasons why birds fly into the sky need to be further explored.