Birds Avoid Mid-Air Collisions By Following These Two Simple Rules

The experience is familiar to everyone. You're walking down a crowded sidewalk, see that you're about to walk into another person head-on, and then you both engage in a graceless left-right-left samba. It's an awkward encounter that seems avoidable, and if people were more like birds, it would be. That's according to new research published last week that describes two simple but crucial adaptations that allow birds to fly in dense flocks without colliding.  

The scientists responsible for the study are from Australia’s University of Queensland, and as part of the team's research, they've been looking to the natural world for ways to develop drones that can avoid mid-air collisions as the skies get more crowded. Birds, they thought, might provide some good lessons. 

"Given that head-on collisions have rarely been observed or reported in birds, we decided to ask whether birds use strategies to avoid them," said Mandyam V.  Srinivasan, the head of the research group, in an email.  

To uncover the birds' internal programming, the researchers constructed a 70-foot-long tunnel outfitted with bright lights so that the test subjects—male Budgerigars or “budgies”—could easily see each other. Using high-speed video cameras to capture every movement, they then released a bird at each end of the tunnel and recorded their near-misses as the budgies barreled towards each other.

Over the course of four days, seven budgie pairs made 102 flights with no mishaps. And when the researchers reviewed the video, they saw that the birds avoided any aerial mishaps thanks to two evolutionary traits. About 85 percent of the time, the birds turned right upon approach. "This seems to be a simple, efficient and effective strategy for avoiding head-on collisions," Srinivasan said. 

The budgies also seemed to decide whether to fly over or under an approaching bird, and the pairs rarely made the same choice—a secondary level of compexity humans don't have to worry about on the sidewalk. How the bird's make these decisions is an open question; the researchers speculate that either each budgie prefers one flying height over the other, or flock hierarchy determines who flies high and who flies low.

For Srinivasan and his team, the results weren't a complete surprise. "It is known, for example, that aircraft pilots are taught to veer to the right when they perceive an imminent head-on collision with another aircraft," he said. "But it was interesting to discover that biology has invented this rule millions of years ago."