Asymmetrical Force Production in the Maneuvering Flight of Pigeons

Downstroke force produced by Rock Doves (Columba livia) as they negotiated an obstacle course was measured using in vivo recordings of delto-pectoral crest strain. Dur- ing this slow (<6 m s-'), maneuvering flight, pigeons produced a series of four to six suc- cessive wingbeats in which the wing on the outside of the turn produced greater peak force than the wing on the inside of the turn, suggesting that the birds maneuvered in a saltatory manner during slow flight. This asymmetrical downstroke force may be used to increase or reestablish bank lost during upstroke, or it may be directed as thrust to compensate for ad- verse yaw or create excess yaw to alter the bird's direction of flight. Continuous production of asymmetrical downstroke force through a turn differs from the traditional model of ma- neuvering flight, in which asymmetrical force is used only to initiate a bank, the forces are briefly reversed to arrest the momentum of the roll and then equalized to maintain the es- tablished bank, and the redirected lift of the wings then effects a turn. Although this tra- ditional model probably describes most turns initiated during fast and gliding flight in birds, it underestimates the complexity of maneuvering during slow, flapping flight, where so- phisticated kinematics and neuromuscular control are needed to change direction effective-