Flight feather#Rectrices

As a control spring ( rectrices ) is also called the tail feathers in birds. In the hunter language, the control springs shock absorbers are called.

The length of the tail feathers in relation to the shape of the wings is an essential feature in flight image and allows conclusions about the way of flying a bird. The control as a summary of the tail feathers is called, can have several functions:

• Control in flight;
• Balance in sitting and walking;
• Support when climbing ( woodpeckers and tree creepers );
• Sound production during courtship ( snipe );
• Signaling effect by shape and color during courtship ( black grouse, peacock, lyre tail).

Some species have only rudimentary control springs ( grebes ). These are arranged in pairs usually. Exceptions are kiwis, emus and cassowaries. Most species have six pairs, but there are also species with only four ( chicken run ) or at the other extreme 16 pairs of tail feathers ( Bulwerfasan ).

In the pictures is clear to see how changing the ratio of the width of inner to outer webs from the inside out.