AIRFLOW SENSORS IN THE AVIAN WING

Abstract

Mechanoreceptors on or near feather follicles in the wings of birds may provide information about airflow over the wing. We studied discharge characteristics of rapidly and slowly adapting mechanoreceptors associated with propatagial covert feathers, slowly adapting receptors within the alular joint and vibration-sensitive receptors of filoplume follicles attached to the follicles of secondary flight feathers during manual feather movements and during airflow over the wing. Dorsal elevation of covert feathers produced an increase in discharge frequency related to the angle of elevation. Extension of the alula produced an increase in discharge frequency related to the angle of extension. Stimulation of receptors located on the distal half of the follicles of secondary flight feathers by airflow over the wing produced a continuous discharge whose frequency correlated with airflow velocity. There is thus abundant sensory input from the wing to the central nervous system. We conclude that birds have the necessary sensor-feather mechanisms in the wing (1) to detect an imminent stall and the location of the separation point of the airflow from the wing's surface, and (2) to measure airspeed by detecting the frequency of vibration of the secondary flight feathers.