Fig. 6. Mean non-acceleration-compensated differential pressure signals for eight positions (P8, P7, P4, P3, S1, S2, S6, S7) along and across the wing. The traces are ordered from distal sites at the top towards proximal sites nearer the bottom, and the synchronising accelerometer trace again appears as the last trace, in green. Values are mean ±1 S.D. (shown in black; N=3 pigeons). Signals for the five sites near the leading edge of the wing are shown in red. Signals for the three pressure sites towards the trailing edge are shown in blue. Periods of downstroke defined by kinematic observations of the wrist are shown as grey for two of the middle three flaps. This shows the close relationship between downstroke timing and the development of `positive' (ventral-to-dorsal) differential pressures, which are used to define downstroke periods shown with underlying grey boxes for take-off and landing. LE, leading edge; TE, trailing edge.