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Flight is a method of moving through the air. To do this, birds use wings with light, hollow bones and feathers on them. Birds have a streamlined body shape, so that they slip through air more easily.
Birds can move by flapping their wings, or they can stay in the same place. This is called hovering, with rapid wing beats, as with the kestrel. Birds that soar use very little energy for it: they use columns of rising hot air to lift them. They glide from the top of a warm air current, and then move on to another warm air current. That way birds like buzzards can fly all day while using little energy.
The fundamentals of bird flight are similar to those of aircraft. Lift force is produced by the action of air flow on the wing, which is an airfoil. The lift force occurs because the air has a lower pressure just above the wing and higher pressure below.