鸟类V形飞行编队的空气动力学奥秘

Researchers using custom-built GPS and accelerometer loggers, developed with funding from the Engineering and Physical Sciences Research Council, (EPSRC), and attached to free-flying birds on migration¹, have gained ground-breaking insights into the mysteries of bird flight formation. The research, led by the Royal Veterinary College, University of London, proves for the first time that birds precisely² time when they flap their wings and position themselves in aerodynamic（空气动力学的） optimal³ positions, to maximise the capture of upwash, or 'good air', throughout the entire flap cycle, while avoiding areas of downwash or 'bad air'.

 

It was previously⁴ not thought possible for birds to carry out such aerodynamic feats⁵ because of the complex flight dynamics⁶ and sensory⁷ feedback required. The study, is published in the journal Nature, on Thursday 16th January 2014.

 

Dr Steve Portugal, Lead Researcher at the Royal Veterinary College, University of London, said: "The distinctive⁸ V-formation of bird flocks has long intrigued⁹ researchers and continues to attract both scientific and popular attention, however a definitive¹⁰ account of the aerodynamic implications of these formations has remained elusive¹¹ until now.

 

"The intricate mechanisms¹³ involved in V-formation flight indicate remarkable¹⁴ awareness¹⁵ 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."

 

Professor David Delpy, Chief Executive 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 collaboration¹⁶ involving inputs¹⁷ not only from many physical and engineering science disciplines, but also the life sciences."

 

The mechanisms that the birds use is achieved firstly through spatial¹⁸ phasing of wing beats when flying in a spanwise ('V') position, creating wing-tip path coherence¹⁹ between individuals which will maximise upwash capture throughout the entire flap cycle.

 

Secondly²⁰, 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 detrimental²¹（有害的） downwash. Such a mechanism¹² would be available specifically to flapping formation flight.

 

Scientists captured the data for the study as the 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 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 30 cm 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 complexity²² for the first time.

 

Dr Portugal and his team worked with the Waldrappteam, a conservation organisation²³ based in Austria, who are re-introducing Northern Bald Ibises into Europe, after being extinct there for 300 years.

 

The 14 juvenile²⁴ birds used in the study were hand-reared at Vienna Zoo by human foster parents from the Waldrappteam. The birds were trained to follow a micro-light 'mother-ship' to teach them their historic migration routes to wintering grounds in Italy. Normally they would learn this from adult birds, and without this help, the birds would not thrive.

 

The birds are currently in Tuscany and the team hopes they will remember the way to what should be their breeding grounds in Salzburg later this year, without the help of the micro-light this time!

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