The biophysics of bird flight: functional relationships integrate aerodynamics, morphology, kinematics, muscles, and sensors

Abstract

Bird flight is a remarkable adaptation that has allowed the approximately 10 000 extant species to colonize all terrestrial habitats on earth including high elevations, polar regions, distant islands, arid deserts, and many others. Birds exhibit numerous physiological and biomechanical adaptations for flight. Although bird flight is often studied at the level of aerodynamics, morphology, wingbeat kinematics, muscle activity, or sensory guidance independently, in reality these systems are naturally integrated. There has been an abundance of new studies in these mechanistic aspects of avian biology but comparatively less recent work on the physiological ecology of avian flight. Here we review research at the interface of the systems used in flight control and discuss several common themes. Modulation of aerodynamic forces to respond to different challenges is driven by three primary mechanisms: wing velocity about the shoulder, shape within the wing, and angle of attack. For birds that flap, the distinction between velocity and shape modulation synthesizes diverse studies in morphology, wing motion, and motor control. Recently developed tools for studying bird flight are influencing multiple areas of investigation, and in particular the role of sensory systems in flight control. How sensory information is transformed into motor commands in the avian brain remains, however, a largely unexplored frontier.

Work loop dynamics of the pigeon (Columba livia) humerotriceps demonstrate potentially diverse roles for active wing morphing

“…The avian wing undergoes substantial shape change during both flapping and gliding (Altshuler et al, 2015;Lentink et al, 2007;Pennycuick, 1968Pennycuick, , 2015. The ability to alter wing shape allows birds to control their aerodynamic efficiency (Lentink et al, 2007), and is also hypothesized to contribute to their maneuverability in flight (Altshuler et al, 2015).…”

“…The avian wing undergoes substantial shape change during both flapping and gliding (Altshuler et al, 2015;Lentink et al, 2007;Pennycuick, 1968Pennycuick, , 2015. The ability to alter wing shape allows birds to control their aerodynamic efficiency (Lentink et al, 2007), and is also hypothesized to contribute to their maneuverability in flight (Altshuler et al, 2015). Some of the change in wing shape is caused by passive tension in soft tissue and inertial forces during flapping, but some shape change is expected to be under active control of the muscles intrinsic to the wing (Chin et al, 2017;Dial, 1992a;Vazquez, 1994).…”

Evolution of avian flight: muscles and constraints on performance

“…A major characteristic of the wings of birds is that they morph extensively during flapping ([16,71,72]; figure 2) and during intermittent flight including bounds and glides [73][74][75]. Such morphing probably has significant effects upon aerodynamic function [72,74,76], but direct tests for such effects in most cases await new research.…”

Comparative Functional Morphology of the Skeletal Forelimb, Pectoral Girdle, and Sternum in Japanese Native Domestic Fowls

“…The structure of the sternum is important in flying birds. The sternal surface provides the attachment area for the M. pectoralis and supracoracoideus, the muscles that function in wing flapping (Yasuda, 2002;Beaufrère, 2009;Altshuler et al, 2015). In the downstroke, the M. pectoralis generates and controls stroke velocity, upward force, and power for flight (Biewener, 1998).…”