New research suggests birds fly in their iconic V-formations in order to arrange themselves in "aerodynamically optimum positions" that take advantage of "good air" (upwash).
The researchers used GPS technology in order to track the movements of migrating birds, a Royal Veterinary College news release reported.
Their research revealed novel mechanisms the birds could use to utilize upwash and avoid downwash (bad air).
"This is achieved firstly through spatial phasing of wing beats when flying in a [spanwize] ('V') position, creating wing-tip path coherence between individuals to [maximize] upwash capture throughout the entire flap cycle," the news release reported.
When the birds fly "streamwize" (behind) spatial anti-phasing of the wing beat occur and doesn't allow wing-tip path coherence or detrimental downwash.
Researchers did not think these types of "aerodynamic feats" were possible until now.
"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," Doctor Steven Portugal Lead Researcher at the Royal Veterinary College, said.
"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," he said.
Researchers have hypothesized that birds' V-formations were related to the struggle to collect upwash, but evidence from free-flying migrating birds was never available for analysis.
The team looked at northern bald ibises their groundbreaking study; these birds are considered to be critically endangered. The team fitted the ibises with "back-mounted [synchronized] GPS and inertial measurement devices." The devices measured the birds' movement and wing flaps during a 43 minute-long flight.
The team found each bird stayed about 45 degrees to the bird ahead and 1.2 meters to the one behind.
"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," Dr. Portugal said.
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," he said.
