New research proves that birds in V formation arrange themselves in aerodynamically optimum positions
15 January 2014
- Precision phasing of flapping wings maximises aerodynamic benefit for birds and their flock-mates
- These accomplishments were not previously thought possible for birds
Groundbreaking Royal Veterinary College research, which appears on the front cover of the journal Nature, proves for the first time that birds flying in a distinctive V formation strategically position themselves in aerodynamically optimum positions, and experience positive aerodynamic interactions that maximise upwash (“good air”) capture.
The data, captured from free-flying migrating birds using specially developed GPS technology, reveals the mechanisms by which birds flying in V formation can both use areas of beneficial upwash while avoiding regions of detrimental downwash (“bad air”).
This is achieved firstly through spatial phasing of wing beats when flying in a spanwise (‘V’) position, creating wing-tip path coherence between individuals to maximise upwash capture throughout the entire flap cycle.
Secondly, when flying in a streamwise (‘behind’) position, birds exhibit spatial anti-phasing of their wing beats, creating no wing-tip path coherence and avoiding regions of detrimental downwash. Such a mechanism would be available specifically to flapping formation flight.
These aerodynamic accomplishments were previously not thought possible for birds because of the complex flight dynamics and sensory feedback that would be required to perform such a feat.
Dr Steven Portugal, (right) Lead Researcher at the Royal Veterinary College and his colleagues studied a free-flying flock of northern bald ibises by following them in a microlight, using specially developed GPS biologging technology to measure the position, speed and heading of all birds in a V formation, and when each bird flapped its wings.
Dr Portugal, said: “The distinctive V-formation of bird flocks has long intrigued researchers and continues to attract both scientific and popular attention, however a definitive account of the aerodynamic implications of these formations has remained elusive until now.
“The intricate mechanisms involved in V formation flight indicate remarkable awareness and ability of birds to respond to the wingpath of nearby flock-mates. Birds in V formation seem to have developed complex phasing strategies to cope with the dynamic wakes produced by flapping wings.”
Theories of fixed-wing aerodynamics have predicted the exact spanwise positioning that birds should adopt in a V formation flock to maximise the gathering of upwash. However there has been a general lack of data from free-flying birds, because of difficulties in measuring the intricate complexity of formation flight, and the lack of appropriate devices to record such information. This means that the precise aerodynamic interactions that birds use have not been identified until now.
Dr Portugal and his team studied a free-flying flock of northern bald ibises (Geronticus eremita), a critically endangered species. They equipped 14 juvenile birds with back-mounted synchronised GPS and inertial measurement devices, which were custom made within the Structure and Motion Laboratory, at the Royal Veterinary College. The team recorded the position and every wing flap of all individuals within the V during 43 min of migratory flight. The precision of these measurements allowed the relative positioning of individuals in a V to be tracked, and the potential aerodynamic interactions to be investigated at a level and complexity not previously feasible.
During a 7 min section of the flight, where most of the flock flew in approximate V formation in steady, level and planar direct flight, researchers found wing flaps occurred at an angle of, on average, 45° to the bird ahead (or behind), and approximately 1.2m behind.
Dr Portugal added: “Here we have shown that ibis flight in V formation does, on average, match predictions of fixed-wing aerodynamics, although of course the flock structure is highly dynamic.
“Birds flying in V formation flap with wingtip path coherence, meaning that their wingtips take the same path to maximise upwash capture. In contrast, birds flying in line flap in spatial antiphase, with wingtip paths maximally separated, to avoid adverse downwash.”
Read more about this research and the technologies behind it on the RVC's Structure & Motion Laboratory's Animal Behaviour Studies pages.
Notes for editors
- Research Reference: Portugal, S.J., Hubel, T.Y., Fritz, J., Heese, S., Trobe, D., Voelkl, B., Hailes, S., Wilson, A.M. & Usherwood, J.R. (2014). Upwash exploitation and downwash avoidance by flap phasing in ibis formation flight.
Nature 505, 399-402. doi:10.1038/nature12939
- Funding was provided by grants from the EPSRC, BBSRC and a Wellcome Trust Fellowship
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