Here is a nice instructive video of the aerodynamic wake behind a flying bat. The bat species is Glossophaga soricina, and it has a forward flight speed of 4 m/s.
In the movie you see the flying bat from behind. The right side of the movie shows the right half of the bat body and its right wing, while the left side of the movie shows the wake generated by the flapping left wing. This wake is calculated using our DPIV system. The colors in it are vorticity strength while the black arrows are the in-plane air velocity vectors.
The movie is slowed down 10 times and it is looped 5 times.