Hummingbirds use active wing pitching during the escape maneuver

Previous studies suggested that wing pitching, i.e., the wing rotation around its long axis, of insects and hummingbirds is primarily driven by an inertial effect associated with stroke reversal of the wings and is thus passive. Here we used 3D computational fluid dynamics to model hummingbird wings during a rapid escape maneuver. The model was based on the body and wing kinematics reconstructed from high-speed videos, and both inertial and aerodynamic effects of the wings were incorporated to resolve time-dependent forces and torques acting on the wings. The results show that although the inertial effect drove the wing flipping at stroke reversal, i.e., similar to hovering, significant power input was required to pitch up the wings during downstroke to enhance aerodynamic force production; furthermore, the net power input could be positive for wing pitching in a complete wingbeat cycle. Therefore, our study suggests that hummingbirds utilize an active mechanism during the maneuver to drive wing pitching and achieve high maneuverability.