In the course of evolution, the vertebrae of the tail were fused into a pigostyle and in their replacement, feathers of different sizes appeared, which formed the tail of the birds. The variety and functions of the tail are possible because of the movements and shapes of the feathers. The tails serve to lift and to steer, like a rudder during flight and landing, tails also serve keeping balance on the go. They also serve as a courtship device. The infographic describes various types of rudder tails. This infographic from the Ábaco collection is part of The Art of Flying series, which also includes those originally titled: Why Do Birds Fly, Adapted Arms, The Secret of Success: Feathers, So is Gliding Flight and So is Flapping Flight.