Fig. 9. Wingtip trace z_tip (open circles) and projected wingspan b' (filled circles; mean values for both wings are mirrored), over a series of wingbeats at U=5, 7 and 10 m s^–1. The bird is flying from right to left and all data is to scale on a 2 mx2 m grid. The start and end of a stroke phase is determined by maximum or minimum wingtip position, z_tip,max and z_tip,min. The downstroke phase is hatched. Data sampled at 1/125 s intervals.