SWARTZ, S. M.; BISHOP, K. L.; ISMAEL AGUIRRE, M. F.; STOCKWELL, E. S.; SKENE, J. A.: Large-scale deformations in the wing bones of flying bats

During flight, bat wings move through space in a three-dimensionally complex way. When we quantify wingbeat amplitudes and frequencies, we capture some proportion of that complexity, but neglect some aspects of kinematics that are potentially important, and that may influence aerodynamics and mechanics. Our three-dimensional kinematic analyses of major anatomical landmarks of the wings of several bat species flying at a range of velocities reveals several examples. In particular, the clavicles, metacarpals, and wing phalanges not only move relative to adjacent bones at their respective synovial joints, they also undergo significant deformation. In all species that we have examined, the clavicles undergo a consistent pattern of bending: the bone is bent in an anteriorly and superiorly convex fashion during the downstroke, and recoils to resting length during the upstroke. As a consequence of this bending, the distance between the proximal and distal ends of the bone decreases by as much as 25% during the wingbeat. The metacarpals and phalanges of the third and fifth digits (the primary chordwise and spanwise supports, respectively) also bend significantly during flight, with considerable variation among species and flight speeds. These previously unobserved skeletal deformations may significantly influence the mechanics, energetics, and aerodynamics of bat flight.