Fig. 2

Kinematic gait analysis of a healthy Willet, based on videos taken at 30 frames/s. Representative step cycles are presented for the walking (0.38 m/s; a, b) and the running animal (1.21 m/s; c, d). In (a) and (c), positions of the left and right foot (tarsometatarso-phalangeal joint) are given as open and closed circles, respectively. A black line indicates the trajectory of the bird’s estimated center of mass (CM); for clarity, areas representing a foot positioned in front of the CM are shaded. CM speed is shown in blue. Average speed, stride length, and the ratio between the lengths of right and left steps are listed. In (b) and (d), the corresponding intertarsal joint angles (top), the stance phases (bottom) of the right (R; black) and left (L; grey) leg, and the right and left duty factors (DF) are shown