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Formation Flight is a V for Victorious Design


The authors of a paper in Nature were stunned. It’s not possible birds could be this smart. What they observed with a flock was so remarkable, they had to remark:

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. We conclude that the intricate mechanisms involved in V formation flight indicate awareness of the spatial wake structures of nearby flock-mates, and remarkable ability either to sense or predict it. (Emphasis added.)

Everyone has wondered at the V formations of migrating birds. Scientists had assumed, but never proved, that the formation provides an energy benefit for the trailing birds, because they could catch the forward-pulling wind in the lead bird’s wake, like a bicyclist drafting behind a truck. Other theories posited that the lead bird was the best navigator, or that the formation limited the number of birds vulnerable to predators.

By “imprinting” some bird chicks to follow them as their proxy “mother,” the team trained them to fly behind a microlight aircraft, much like the stars of the classic documentary Winged Migration. They installed loggers on the birds, then filmed them in flight, collecting data not only on their positions in the formation, but on the motion of their wingtips.

Here we show that individuals of northern bald ibises (Geronticus eremita) flying in a V flock position themselves in aerodynamically optimum positions, in that they agree with theoretical aerodynamic predictions. Furthermore, we demonstrate that birds show wingtip path coherence when flying in V positions, flapping spatially in phase and thus enabling upwash capture to be maximized throughout the entire flap cycle. In contrast, when birds fly immediately behind another bird — in a streamwise position — there is no wingtip path coherence; the wing-beats are in spatial anti-phase. This could potentially reduce the adverse effects of downwash for the following bird.

What this implies is the bird’s ability to sense the invisible wake structures behind a leading bird, including the ability to predict its moment-by-moment changes, and then orient itself in the optimum position and flap its wings in time to take advantage of the upwash and avoid the downwash. The birds located themselves within the V formation in positions that were completely predicted by fixed-wing aerodynamics: in other words, to be in the best possible spot to take advantage of the upwash from the bird in front.

The “most interesting finding,” though, was about wingtip phasing. The birds even time their flaps as a function of wavelength between updrafts. This is explained nicely in a short video on Nature News, “Come Fly with Me,” where lead investigator Steve Portugal and his assistant Jim Usherwood describe the loggers, show the birds in flight, and illustrate the aerodynamic principles in simple animations and hand motions.

Nature News explains how birds could compensate in real time:

When the flock got it right, each following bird delayed its wingbeat by just enough to spread a wave of synchrony through each arm of the V. When they got it wrong and a following bird drifted directly behind the bird in front, the follower registered the problem and adjusted the timing of its flaps so that it did not become tangled in the powerful downdraught of the same vortex.

Since all the birds were the same age, none had any prior experience of the migration route, which had been altered by the researchers on the microlight aircraft to avoid the Alps. This rules out the theory that the lead bird was the best navigator. Even though forming the V and maintaining it is not easy, the ibises knew instinctively how to get it right for achieving the optimum energy efficiency, even without the benefit of parent birds to teach them.

Michael Habib, writing for The Conversation, understands that the birds must be doing “maths on the fly” to achieve this feat.

Aerodynamic theory predicts birds should save energy if they carefully adjust their position and flapping speed in a formation. This made some scientists question whether birds have the required sensory precision to achieve this feat in mid-air.

In a study just published in Nature, an international team led by Steven Portugal of the Royal Veterinary College in London shows that birds defy these expectations: they really can fine-tune their flight formations to be more efficient.

Although the findings were made with one species bred in captivity, other birds likely use the same technique, Habib notes. But “How these birds are able to sense and predict such subtle changes in air flow is still a mystery.” Either they have sensory abilities we are not aware of, or can do the required math on the wing. “Either way, it is clear that birds still have a lot to teach us about their abilities and success as flying animals.”

This sentiment is echoed by the BBC News with more diagrams and video, calling the birds’ feat “exciting” and “amazing.” Another Nature News piece is titled, “Precision formation flight astounds scientists.”

“The implications of this research could be quite far-reaching,” Portugal explains in the video. “So, for example, airlines have been investing heavily to try to understand how the birds can get so close together to take advantage of this upwash. They want their planes doing the same thing — of course something that the birds have been doing forever, and just doing intuitively.”

Here, again, we see biomimetics leading science forward — intelligent design reverse-engineering natural design, in this case, a quite “astonishing” and “remarkable” one.

Related Stories

Cuckoos stay on course: The Max Planck Institute reports that the cuckoo — another long-distance flyer — hardly deviates from its route, though flying 16,000 kilometers per year. “Despite the enormous distances” in their path from Sweden to northern Africa, “the routes of the individual birds hardly differ from one another,” implying that the birds “do not rely solely on an inborn compass-clock-navigation ability, but use additional orientation aids.”

Findings like these are made possible by miniature geolocators that are light enough for the birds to carry without slowing them down. “The flight of the cuckoo is precisely tailored to local conditions for feeding and breeding,” the article says, even though they cross the Sahara en route, requiring a particularly “astonishing sense of direction” to do so. Since they fly mostly at night and cannot rely on guides, the researchers are struggling to understand what innate maps and navigation aids allow them to stick so closely to their flight plan.

Falcons strategize in flight: How falcons stalk their prey in mid-air is the subject of an article on Live Science by Denise Chow. Once again, microlight technology is bringing avian feats to light:

To gain insight into the hunting practices of falcons, researchers at Haverford College in Haverford, Pa., outfitted falcons across the United States and Europe with miniature helmet- and backpack-mounted video cameras to record footage of raptor attacks in action.

The scientists found that falcons stalk their prey by maneuvering through the air in such a way that the target appears stationary in their field of view. This lethal attack strategy, described online today (Jan. 15) in The Journal of Experimental Biology, helps falcons effectively intercept their prey without having to tail closely behind their victims.

The helmets make the birds look even more fearsome than usual. The embedded video allows readers to fly along with the raptors as they hone in on crows unlucky enough to get in the crosshairs.

Because dragonflies and bats adopt similar strategies, one of the researchers surmised, “There seems to be an evolving picture here.” But how could that be? The common ancestor of those creatures would have had to be extremely remote, unless all three achieved this design by the miracle of “convergent evolution.” Any “evolving picture” is a figment of the researcher’s imagination.

Longest European migration: Geolocators allowed scientists to determine that the red-necked phalarope goes the longest distance of any European migratory bird, Jennifer Viegas reported on Live Science. Its epic round-trip journey of 16,000 miles takes it “from the island of Fetlar in Shetland, Scotland, across the Atlantic, south down the eastern seaboard of the United States, across the Caribbean, and Mexico, ending up off the coast of Peru.” While no match for the Arctic tern’s annual distance of 44,000 miles — see Flight: The Genius of Birds — it’s still an impressive feat, considering that the birds fly nonstop for six months. In an unusual role reversal for birds, the males of this species sit on the eggs while the females strut their bright feathers to attract mates. Like the bald ibis, the red-necked phalarope is an endangered species whose navigation feats are worth conserving.

Photo source: Alyson Hurt/Flickr.

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