Effects of wing damage and moult gaps on vertebrate flight performance.

Vertebrates capable of powered flight rely on wings, muscles that drive their flapping and sensory inputs to the brain allowing for control of the motor output. In birds, the wings are formed of arrangements of adjacent flight feathers (remiges), whereas the wings of bats consist of double-layered skin membrane stretched out between the forelimb skeleton, body and legs. Bird feathers become worn from use and brittle from UV exposure, which leads to loss of function; to compensate, they are renewed (moulted) at regular intervals. Bird feathers and the wings of bats can be damaged by accident. Wing damage and loss of wing surface due to moult almost invariably cause reduced flight performance in measures such as take-off angle and speed. During moult in birds, this is partially counteracted by concurrent mass loss and enlarged flight muscles. Bats have sensory hairs covering their wing surface that provide feedback information about flow; thus, wing damage affects flight speed and turning ability. Bats also have thin, thread-like muscles, distributed within the wing membrane and, if these are damaged, the control of wing camber is lost. Here, I review the effects of wing damage and moult on flight performance in birds, and the consequences of wing damage in bats. I also discuss studies of life-history trade-offs that make use of experimental trimming of flight feathers as a way to handicap parent birds feeding their young.