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Fig. 5. Deviations in the Y direction (up/down) of points on the neck. The
deviations are relative to the mean swimming direction of the birds (red
broken arrow). The Y axis is the same as described for
Fig. 4B, and the X
axis is the same as described for Fig.
2. The points are the tip of the bill and the base of the neck.
Several points are missing at the end of the cycle, as the birds exited the
view of the camera. It is clear, however, that the tip of the bill moves
differently from the body (represented by the base of the neck), ascending
when the body descends during the stroke phase and vice versa during
the end of the glide and the recovery phase.