Analysis of a 180-degree U-turn maneuver executed by a hipposiderid bat

Application of a novel deep learning-based 3D videography workflow to bat flight

Studying the detailed biomechanics of flying animals requires accurate three-dimensional coordinates for key anatomical landmarks. Traditionally, this relies on manually digitizing animal videos, a labor-intensive task that scales poorly with increasing framerates and numbers of cameras. Here, we present a workflow that combines deep learning-powered automatic digitization with filtering and correction of mislabeled points using quality metrics from deep learning and 3D reconstruction. We tested our workflow using a particularly challenging scenario: bat flight. First, we documented four bats flying steadily in a 2 m3 wind tunnel test section. Wing kinematic parameters resulting from manually digitizing bats with markers applied to anatomical landmarks were not significantly different from those resulting from applying our workflow to the same bats without markers for five out of six parameters. Second, we compared coordinates from manual digitization against those yielded via our workflow for bats flying freely in a 344 m3 enclosure. Average distance between coordinates from our workflow and those from manual digitization was less than a millimeter larger than the average human-to-human coordinate distance. The improved efficiency of our workflow has the potential to increase the scalability of studies on animal flight biomechanics.

Role of wing inertia in maneuvering bat flights

The role of aerodynamics and wing inertia on the motion dynamics for the maneuvering flight of two bats from two species of roundleaf bats,H. armigerandH. prattiare investigated. Comparative studies among a straight flight, two ascending sweeping right turns, and a U-turn reveal that inertial forces play an essential and sometimes crucial role in the maneuvers. The translational trajectory of the bat is mostly driven by aerodynamic forces generated by the wings along the flight path, whereas inertial forces for the most part drive the intra-cycle fluctuations. However, inertial forces are found to contribute non-trivially to the ascending motion of theH. armigerduring the sweeping turn and the U-turn. The roll maneuver is found to be primarily driven by aerodynamic asymmetries during flight, whereas the yaw maneuver is primarily driven by imbalances in wing inertial moments. Inertial moments resulting from Coriolis and centrifugal forces are found to play an important role in accurate yaw prediction. The moment due to Coriolis force plays a very prominent role in predicting the correct yaw angle during the extreme 180° U-turn.

Turning-ascending flight of a Hipposideros pratti bat

Bats exhibit a high degree of agility and provide an excellent model system for bioinspired flight. The current study investigates an ascending right turn of a Hipposideros pratti bat and elucidates on the kinematic features and aerodynamic mechanisms used to effectuate the manoeuvre. The wing kinematics captured by a three-dimensional motion capture system is used as the boundary condition for the aerodynamic simulations featuring immersed boundary method. Results indicate that the bat uses roll and yaw rotations of the body to different extents synergistically to generate the centripetal force to initiate and sustain the turn. The turning moments are generated by drawing the wing inside the turn closer to the body, by introducing phase lags in force generation between the wings and redirecting force production to the outer part of the wing outside of the turn. Deceleration in flight speed, an increase in flapping frequency, shortening of the upstroke and thrust generation at the end of the upstroke were observed during the ascending manoeuvre. The bat consumes about 0.67 W power to execute the turning-ascending manoeuvre, which is approximately two times the power consumed by similar bats during level flight. Upon comparison with a similar manoeuvre by a Hipposideros armiger bat (Windes et al. 2020 Bioinspir. Biomim. 16, abb78d. (doi:10.1088/1748-3190/abb78d)), some commonalities, as well as differences, were observed in the detailed wing kinematics and aerodynamics.