Meeting Abstract
Previous work indicates that strong coupling of elbow and wrist motion in birds results in an outsized influence of elbow angle on overall wing morphing. The muscular morphology of the avian wing that controls elbow flexion is highly unique. In addition to the biceps, there are two muscles unique to birds with attachment points and tendinous properties that are highly unusual relative to other vertebrates. This elbow flexion system has no parallel in other vertebrates, is highly diverse across avian species, and yet has not been studied in close detail. We sought to answer fundamental questions on what roles each muscle performs in flight, how the muscles in this system interact in different modes of flight, and what possible scaling relationships may bound and drive the morphological variation of this system. We collected in vivo electromyography and kinematics measurements on European Starlings in wind tunnel flights designed to elicit both gliding and level flapping behaviors. These investigations were coupled with isolated muscular studies to characterize the activation dynamics, force production, and torque production of the wing muscles of interest. We show that the three passerine elbow flexors exhibit a robust pattern of sequential activation that is closely rooted to their anatomical arrangement and muscular dynamics, and that the specific flexor muscles unique to birds utilize favorable lever arms to generate higher torques from comparatively lower muscle masses than traditional elbow flexors. This study provides a view of the interrelation between muscular morphology and coordination, and how a highly specialized avian muscular system is used to generate and control flight.
