Figure 4. Velocity of the body in the duck frame of reference.

The average velocity of the body shown as components along the three axes fixed on the duck. Ux, Uy and Uz are the component of velocity along the long, lateral and dorsoventral axes of the body respectively (see Fig. 2 and Appendix S2). The time (horizontal) axis is normalized time within a paddling cycle. The horizontal white and black rectangles at the top illustrate the division of the paddling cycle into the power and recovery phases. Data averaged from N = 4 birds, ± SD.