People: Steven Portugal, Alan Wilson, Jim Usherwood, Tatjana Hubel

  • 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 appeared on the front cover of the journal Nature (16 January 2014), 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”).

Ibises flying in formation
Ibises flying in formation (photo credit: Markus Unsöld)

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 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.

Steve 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.

Data logger being attached to one of the ibises
Data logger being attached to one of the ibises

“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.

The 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.

Ibises flying in V formation behind the microlight
Ibises flying in V formation behind the microlight (photo credit: Markus Unsöld) 

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.

Steve 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.

Read the paper:

Upwash exploitation and downwash avoidance by flap phasing in ibis formation flight

Steven J. Portugal,Tatjana Y. Hubel, Johannes Fritz, Stefanie Heese, Daniela Trobe, Bernhard Voelkl, Stephen Hailes, Alan M. Wilson & James R. Usherwood

    Nature 505, 399–402

    doi:10.1038/nature12939

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