Fig. 4. Velocity fields in the wake of chukar Alectoris chukar during WAIR as revealed using DPIV. Backgrounds in (A,C,E) illustrate the bird and incline and in (B,D,F) represent vorticity (). Transparent red loops represent an assumed 3D shape of vortex rings as inferred from concentrations of about and in the DPIV images. (A,B) Baby, ascending at 65°. (C,D) Juvenile ascending at 90°. (E,F) Adult, ascending at 80°. Both starting and ending vortex cores, evident as concentrations of ^– and ⁺, respectively, are visible for the wake of the juvenile, whereas the wings and body mask ending vortices in baby and adult. Erroneous vectors due to the DPIV algorithm are apparent above the back of the adult in E.