Wing-flapping develops in chickens made flightless by feather mutations

Two lines of mutant, domestic chickens (scaleless and delayed feathering), flightless because they lack flight feathers, were used to evaluate the influence of flight-related experience and adaptation on the development of wing-flapping. Most testing was at 13 days because normally feathered control chicks of this age flap at adult rates and can fly. By 13 days, the wing-flapping rates of the flightless, mutant chicks and the normally feathered and flight-competent control chicks were similar. Therefore, normal adult rates of wing-flapping developed in the absence of flight-related behavioral consequences. Drop-evoked wing-flapping was probably initiated by vestibular mechanisms: feather-related mechanoreceptor and visual cues were not necessary because flapping was initiated by naked, scaleless chicks which were deprived of visual input by masking their eyes or by testing in a darkened room. The possible role of feather mutations in the evolution of avian flightlessness is also considered.