06 October 2009
New Lab Publication in J Exp Biol
In a new paper, published in J Exp Biol 212: 3365-3376 (2009), Christoffer Johansson and Anders Hedenström report on wake properties of blackcaps (Sylvia atricapilla) studied on the Lund University wind tunnel. They use a high speed stereo-3D PIV system to get information from the entire wake behind the flying bird. It was found that the wake geometry was slightly more complicated that previously thought about passerine birds. This is mainly due to that the PIV system used is capable of detecting more subtle features of the wake, than with previous 2D visualization. Another twist is that one bird accidentally molted its tail, but flying without a tail did not cause any dramatic changes as to the bird's wake. The function of the tail, whether it is a lift generating surface or if it works as a splitter plate that reduces the drag, remains unclear. New experiments will hopefully teach us more about what birds have tails for.