Fig. 7. Occurrence of foot propulsion as a function of position inside the obstacle course. Each chart represents a maneuvering difficulty level labeled according to the horizontal distance between the adjacent barriers (cm) (Fig. 1). Black bars denote the adjusted horizontal positions within the obstacle course where active paddling (stroke) was observed in the video. Note that the birds are less likely to paddle while entering the obstacle course (horizontal axis=0) and more likely to paddle above the second barrier (horizontal axis=0.5). Vertical arrows denote the positions of the barriers (0, 0.5 and 1.0) on the adjusted horizontal axis.