Fig. 4. Reconstruction of the vortex wake from a complete wingbeat at different spanwise locations: (A) arm wing (X in Fig. 2), (B) mid-hand (Y in Fig. 2), (C) outer-hand (Z in Fig. 2), and (D) body (LR in Fig. 2). The mean flow has been subtracted so the reference frame is in still air, as though the bird has passed from right to left. The spanwise vorticity, _y(x,z), is colour coded on a constant scale, symmetric about 0 s^–1. Velocity vectors are drawn with 1/3 of the actual density.