NBI shows why birds fly in V

Many bird species have developped refined flying strategies drawing an almost perfect V in flight. It has been traditionally assumed that this tactic minimizes energy costs, but until now, there was not enough scientific evidence to explain how it works.  

A team from Austria, Germany and United Kingdom has shown how NBI individuals have developed a range of phasing strategies in order to optimise turbulences produced by flapping wings. Individuals flying in a V-flock position themselves in aerodynamically most favourable positions, in accord with theoretical aerodynamic predictions. Besides, birds flaps spatially in phase, thus enabling optimal upwash capture throughout the entire wing-beat cycle. In contrast, when birds fly immediately behind another bird, they flap in anti-phase. This could potentially reduce the adverse effects of downwash for the following bird. These aerodynamic accomplishments require complex flight dynamics and sensory feedback to optimise the benefits and reduce the loss due to turbulences made by preceding flock mates.

Source:

Portugal, S.J., T.Y. Hubel, J. Fritz, S. Heese, D. Trobe, B. Voelkl, S. Hailes, A.M. Wilson & J.R. Usherwood. 2014. Upwash exploitation and downwash avoidance by flap phasing in ibis formation flight. Nature, 505: 399–402