HEDRICK, TL; Univ. of Washington: Low-speed turning kinematics of the rose-breasted cockatoo

Maneuvering flight is a crucial component of the natural behavior of the majority of bird species. This study couples 250 Hz 3D kinematics with bilateral electromyograms (EMGs) from eight flight muscles to examine the aerodynamic and neuromuscular mechanisms birds employ to initiate and control turns. Recordings were made from six wild caught rose-breasted cockatoos (Eolophus roseicapillus) trained to fly through an L-shaped flight corridor, making a 90-degree turn midway through each flight. The corridor, constructed of lightweight netting, was 1 m wide by 2.2 m high with one 2 m and one 3 m segment forming the L. Three 250 Hz video cameras were arrayed around the outside of the flight corridor, allowing 3D reconstruction of the flight kinematics. Prior analysis of the EMG data found large asymmetries in biceps muscle activation at the beginning and end of each turn, leading to a preliminary mechanistic hypothesis of turning via left-right asymmetries in wing area. Subsequent analysis of the 3D flight kinematics in conjunction with the EMGs both supports and refines this hypothesis. The cockatoos turned by first rolling in the direction of the turn, flapping symmetrically through the turn and finally rolling back to level at the end of the turn. Rolls were typically initiated in the second half of the downstroke preceding the turn and continued at high angular velocity through the subsequent upstroke, concurrent adverse yaw was also observed. Following the first wingbeat of the turn, the cockatoos continued to roll with decreasing angular velocity until the midpoint of the turn, reaching a maximum roll angle of approximately 70 degrees before beginning to roll back to level. Rolls were initiated during the wingbeat containing the biceps activation asymmetry, which was concurrent with a reduction in wing area.