Birds can gain altitude, as stated by Leonardo, by "[raising] the shoulders and [beating] the tips of the wings towards itself, thus condensing the air that stands between the tips of [its] wings and itself". He also describes the flight of a kite as seeking a wind current. When the winds are high, one will see the bird very high in the sky, but when the winds are low, the bird stays closer to the ground. Leonardo describes how a bird rests in the air, after flapping its wings to gain altitude, by gliding downward to the ground.