Fig. 2. Variation in velocity during one paddling cycle. The plot was obtained from one video sequence (Bird 5) and smoothed by a stepwise 5-point moving average for easy viewing. The plot shows the kinematic parameters defined by Weihs (1974) for the burst-and-glide model (L₁, L₂, U_i, U_f), and the additional parameters defined in the present study (L_p, L_g, L_r, U_r, t_p, t_g, t_r); see List of symbols for the description of each parameter. The bottom bar indicates the division of the paddling cycle into three stages based on the motion of the feet relative to the body (stroke, glide and recovery). Average swimming speed for this cycle was 1.72 m s^–1. Note that the bird did not swim at a constant speed but rather accelerated during the power stage and decelerated during the glide and recovery stages in a burst-and-glide swimming pattern.