Meeting Abstract
Birds are well known for their ability to fly. To avoid injury, a successful flight also demands a safe and precise landing. Previous studies have shown that birds regulate landing through a visual collision avoidance strategy, known as general tau theory. Tau theory predicts that collision can be avoided by regulating tau, the distance to collision divided by the rate of change of that distance. Birds not only regulate tau, but tend to keep the rate of change of tau itself constant; this is termed tau-dot constant. However, most studies on the biomechanics and control of landing in birds have been conducted with a perch in a laboratory setting, and its relationship to other landing modalities is unknown. In this study, we filmed birds landing in the wild to test if regulation of tau is present in a natural habitat. We filmed mallards (Anas platyrhynchos) landing on water at a local pond using three video cameras (GoPro Hero 4), with recordings synchronized post-hoc using sound. We used a 0.94 m wand to spatially calibrate the volume in conjunction with Argus 3D tracking software. The kinematics of landings were obtained by manually digitizing natural landmarks on the bird. Based on 23 landings, mallards exhibit a diverse range of landing trajectories, with approach angles as great as 40° relative to the water surface, and impact speeds from 0.8 to 7.5 m/s. Tau is highly linear regardless of landing trajectory or impact speed, with a mean linear correlation coefficient of -0.983 (p< 0.001). These results suggests that mallards use tau and tau-dot constant strategies, as seen in perch landing behavior.
