Ibises' Flight Precision Stuns Researchers
PARIS, Jan 15, 2014 (AFP) - Ibises flying in a V formation synchronise the flapping of their wings with a degree of precision previously thought impossible, astounded researchers said Wednesday.
A team that measured every single wing beat of 14 birds during 43 minutes of a migratory flight found that each animal positioned itself in just the right place in relation to the others, and timed its flaps so as to gain the most aerodynamic advantage.
From the lone leader at the point of the V, the ibises fanned out to the back and side at an angle of about 45 degrees, and flapped their wings in phase.
This allowed each bird to gain as much lift as possible from the small area of air "upwash" in the wake of the preceding bird, while they carefully avoided areas of "downwash" that would push them earthward.
"We were amazed," Steven Portugal of the Royal Veterinary College in Hertfordshire, England, told AFP of the results published in the journal Nature.
"The amazing control and coordination required for the birds to stay in position and exhibit this precise flap timing was, we thought, too hard and not possible."
V formation saves energy
Scientists have long concluded that geese, pelicans and other flocking species probably fly in a V-shaped formation to save energy, riding on drafts created by those in front.
But the degree of precision with which this is achieved was not previously understood.
"We are the first... to identify the aerodynamic interactions between individuals within a V, and to record the mechanism that birds in a V use to capture upwash (rising air)," Portugal said.
The team of researchers from Britain, Austria and Germany used 14 northern bald ibises, hand-reared at the Vienna Zoo, for the experiment.
The endangered birds had human foster parents whom they had been taught to follow in a microlight airplane -- thus learning their migratory route to their wintering grounds in Italy.
For the test, each of the birds had a lightweight GPS (Global Positioning System) locator mounted on its back, as well as an "accelerometer" to measure how often it flapped its wings, and how hard.
The birds and their foster parents then set off from Salzburg, Austria, to Italy's Tuscan region.
A total of 180,000 wing flaps were measured during a 43-minute section of the journey.
"What we totally weren't expecting was that they might be paying attention to the flap-phasing of the bird ahead," Portugal's colleague and study co-author James Usherwood said in a Nature video.
Amazingly, they found the trailing bird's wing flaps closely followed the pattern of the draft created by the preceding bird -- it can be visualised as an unbroken wave formed as the wings flap up and down.
The scientists found that if a bird in the V is a full wavelength behind its leader, their wing positions match (both tips up, or both down).
But half a wavelength behind, its wings would be in the inverse position of the bird ahead if it.
The findings revealed a "remarkable awareness and ability of birds" to match their flock mates' wing flaps, Portugal said.
The research may have implications for the aviation industry.
"Airlines have been investing heavily to try and understand how birds can get so close together to take advantage of this upwash -- they want their planes to do the same thing," he said.
Allied bomber pilots in World War II are rumoured to have noticed fuel savings when flying in a V formation.
"Understanding how birds can behave together to experience positive aerodynamic interactions can allow us to save fuel in such flying machines" as drones or ornithopters, which mimic wing-flapping insects, Portugal said.
Image via Markus Unsöld, AP