Fig. 1. Wake velocity and vorticity (s^–1) plots of the near wake in the streamwise plane [x, z] for the outer wing (A), inner wing (B) and centre of the body (C) at a flight speed 1.5 m s^–1, and in the transverse plane [y, z] at mid-downstroke (D), mid-upstroke (E) and end of upstroke (F) at a flight speed of 4 m s^–1. The white arrow indicates the vortex ring generated at the outer wing during the end of the upstroke. Vorticity is scaled according to the colour bar to the right of each row and vectors are scaled according to the reference vector (modified from Hedenström et al., 2007).