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A Theory On Why Birds Don't Crash Into Each Other

Future anti-crash systems could take a lesson from birds.

Starling murmurations are one of the most underappreciated feats of nature. Hundreds, if not thousands, of birds will flock together across the sky, creating an undulating mass of feathers in flight. Their movements are seemingly random, yet none of them ever collide, as if their complex dance had been cleverly choreographed.

Murmurations are an extreme example of birds' uncanny knack for synchronized flight. You've probably seen the iconic V-formation of migrating geese, or the graceful soaring of seabirds over water. But one thing that's continued to stump biologists is how, exactly, airborne birds manage to avoid crashing into one another.

A starling murmuration. Image: Flickr/Donald Macauley

"Birds must have been under strong evolutionary pressure to establish basic rules and strategies to minimise the risk of collision in advance," said Mandyam Srinivasan, a professor of visual and sensory neuroscience at the University of Queensland, in a statement.

The mechanics of bird flight fascinated Srinivasan, so he decided to conduct a series of traffic experiments using budgerigars, or common pet parakeets, to model their aerial patterns. What he observed was an unwavering predilection for veering right, which was able to keep traffic flowing smoothly, so to speak. No crashes occurred over the course of 102 flights.

Could the riddle behind synchronized bird flight really be this simple?

According to Srinivasan, "no previous studies have ever examined what happens when two birds fly towards each other." He and two other colleagues used high-speed cameras to record the flights of 10 budgerigars released from opposite ends of a tunnel. The team's findings were published this week in PLOS One, and concluded that budgerigars use a two-pronged technique for achieving crash-free flight.

First, they'll veer right when confronted by another bird mid-air. Second, they'll choose to fly higher or lower than the other bird, "according to a preset preference." What influences a budgerigar's altitude bias, we still don't know. But the authors theorized that social hierarchy might have something to do with it.

"It might be that their position in the group hierarchy determines their flight height. This is a question for further research," Srinivasan added.

Still, while these findings offer a fascinating glimpse into budgerigar flight, they don't explain the aerial mechanics of all birds. Parakeets exhibit different social structure than, say, starlings or albatross, so it's difficult to conclude what role behavior plays in synchronized flight across the avian spectrum. It's also unclear whether pet budgerigars were used for this study, which raises questions over how flight patterns may differ between wild and captive individuals.

Previous investigations into bird flight have produced equally remarkable conclusions, however. For example, Andrea Cavagna, a physicist at the National Research Council of Italy, found that starlings developed a buddy-system for controlling the movement of murmurations. In a split-second, one individuals can signal many, steering the mass away from a predator or around obstacles.

Another study, led by David Williams of the University of Washington, suggested that pigeons navigate their surroundings using various flight postures, determined by the positioning of their wings. By manipulating the aerodynamics of their bodies, pigeons are able to zip around chaotic environments, such as busy cities, at incredibly high speeds.

Pigeons folding their wings to squeeze between obstacles. GIF: Ariah Kidder

Srinivasan's research was conducted in partnership with Boeing Defence Australia, and could be used to improve anti-crash systems on jets, airplanes, or even drones. "As air traffic becomes increasingly busy, there is a pressing need for robust automatic systems for manned and unmanned aircraft, so there are real lessons to be learned from nature," he said.

"While we can't say how birds solve the problem of switching to different altitudes, we can propose some simple strategies for autopilot systems and unmanned aerial vehicles to prevent head-on collisions."

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