What powers the flight of soaring birds? (See \"The Soaring Flight of Birds,\" by C. D. Cone, Jr., Scientific American, April 1962, p. 130.)

The airflow up in the high altitude is not uniform. So, the velocities of the adjacent air flow are not same. According to Bernoulli’s equation, the pressure is large when the velocity is small and the converse. When the soaring birds are in such high, the pressure difference below and above their wings vary. It is such that the pressure is larger above the wings of the soaring bird than below it. Thus, a dynamic lift force generates and helps the bird to soar high in the sky. Therefore, the flight of the soaring bird is propelled by the air flow.