BISHOP, K.L.; SWARTZ, S.M.; STOCKWELL, E.F.; SKENE, J.A.; ISMAEL-AGUIRRE, M.F.: Three Dimensional Complexity of Bat Wing Movements

The kinematics of vertebrate flight have traditionally been described in terms of a few, simply measured parameters, i.e. wing beat frequency, stroke amplitude, and stroke plane angle, but how these parameters affect the aerodynamics of flight is not well understood. Since the wings of bats are significantly more flexible than those of birds, these measurements may have different aerodynamic meaning in bats as they do not take into account the three dimensional complexity of the bat wing during flight. Using synchronized, high-speed video, we have conducted a three-dimensional analysis of wing beat kinematics in several species of bats flying at a range of speeds in a wind tunnel. Using these video data, we have examined how wing beat frequency varies with forward speed and body mass. We were also able to track the trajectories of the wing tip and several other landmarks on the wing in three dimensional space in order to ascertain the amount of variability in total excursion of the tip. This analysis allows us to evaluate the usefulness of stroke amplitude and stroke plane angle as predictors of aerodynamic performance in bat flight. We believe that there is much information to be gained from this three-dimensional approach that is not available using traditional methods.