Fig. 12. A comparison of the mean proximal wing circulation during the upstroke and the mean distal wing circulation during the downstroke for the doves (A) and cockatiels (B) over the full range of flight speeds examined. Values are means ± S.D. (N=2). for each species at each speed. The shaded region indicates the range of speeds in which downstroke and upstroke circulation are approximately equivalent, resulting in a continuous-vortex wake.