How Pigeons Avoid Collisions

Birds are good at not crashing into stuff. So good that it’s easy to take their ability to avoid trees, telephone wires, and other birds for granted. But Harvard biologist David Williams wanted to know how, exactly, birds avoid close calls.

So Williams set up an obstacle course in his lab: a series of white poles spaced closely together. He watched as pigeons tested their mettle, catching their movements with high-speed cameras as they flew around the room, and through the gaps between the poles.

Reviewing the footage, he found that agile fliers adopt one of two postures to avoid a collision, he reports in the journal Proceedings of the National Academy of the Sciences: wing pausing and wing folding: 

In the “paused” configuration, the pigeons stopped flapping right before the obstacle, exactly at the moment when their wings were up above their bodies, at the very top of the stroke. With their bodies thus tall and skinny, rather than wide, they could pass through. In the “folded” configuration, the birds hugged their wings close to their body as they darted through the opening, again minimizing their width.

While the “paused” posture is speedier, as it’s less disruptive to flight, the “folded” posture is safer: with its wings wrapped around it’s body, the bird is better protected in the event of a crash.

Surprisingly, these two tricks seemed to be the only ones the pigeons had up their, erm, wings, Williams explained to Harvard news:  “We thought it would be catch-as-catch-can, and it’s not.” The researchers didn’t document the birds rotating, or trying to pass with one wing up and one wing down.

That doesn’t mean the birds don’t employ other obstacle-avoidance positions. Next up, Williams will test the pigeons on horizontal obstacles that mimic tree limbs and record their fancy flight work.