Custom-built GPS and accelerometer loggers have uncovered ground-breaking new insights into the flying-V formation used by birds.
Research led by the Royal Veterinary College at University of London has proved for the first time that birds precisely time when they flap their wings and place themselves in aerodynamic optimal positions when flying in formation.
It was previously not thought possible for birds to carry out such aerodynamic feats because of the complex flight dynamics and sensory feedback required, but the study found they position themselves to maximise the capture of upwash, or ‘good air’, throughout the entire flap cycle, while avoiding areas of downwash or ‘bad air’.
Lead researcher Dr Steve 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.”
The scientists captured the data as the flock of 14 juvenile Northern Bald Ibises birds flew alongside a micro-light on their migration route from their summer birthplace in Austria to their wintering grounds in Tuscany, Italy.
The study, published in the journal Nature and developed with funding from the Engineering and Physical Sciences Research Council (EPSRC), is the first to collect data from free-flying birds and was made possible by the logging devices custom-built at the Structure and Motion Laboratory at the Royal Veterinary College.
The light-weight, synchronised, GPS and inertial measurement devices, recorded within up to 30cm accuracy where a bird was within the flock, its speed, and when and how hard it flapped its wings. The precision of the measurements enabled the aerodynamic interactions of the birds to be studied at a level and complexity for the first time.
Professor David Delpy, chief wxecutive of the EPSRC, said: “This is a fascinating piece of research, providing a scientific answer to a question that I suspect most people have asked themselves – why do birds fly in formation? The results will prove useful in a variety of fields for example aerodynamics and manufacturing.
“The research is an excellent example of an international collaboration involving inputs not only from many physical and engineering science disciplines, but also the life sciences.”
The mechanisms that the birds use is achieved firstly through spatial phasing of wing beats when flying in a spanwise (‘V’) position, creating wing-tip path coherence between individuals which will 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.
Dr Portugal and his team worked with the Waldrappteam, a conservation organisation based in Austria, who are re-introducing Northern Bald Ibises into Europe, after being extinct there for 300 years.