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Fig. 7. The back-sweep arch of the foot of the great cormorant, relative to the
body, in the XY plane (red symbols). The surface of the foot is
represented by the center of hydrodynamic forces (see text). Each point is the
mean from all birds (N=9). The points shown belong to the stroke
phase and are spaced by 0.02 s intervals (the time frame between fields) and
sequenced by the adjacent numbers. The position of the foot is presented
relative to the position of the center of mass located at point (0,0) and
marked by `x'. The bird swimming direction is from left to right. During
the stroke phase, the body is at maximal tilt, as indicated by the orientation
of the red figure. The arch of the foot trajectory is vertical, partly due to
the fact that the body is tilted. The vertical motion relative to the center
of mass is in the first 0.12 s of the stroke phase (fields 1–6). The
white open symbols are the same data as the red but rotated at 15°
counter-clockwise to demonstrate a hypothetical foot trajectory when the
cormorant body aligns with the swimming direction (orientation of the white
figure).
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