Why Pigeons Don't Crash: a Mystery of Cityscapes Explained

Birds don't seem all that smart. Despite being experts in the air, flying better than anything humanity has ever constructed, they still collide with a stunning number of cars and planes. Past studies have even revealed that a whopping 340 million birds have fatal run-ins with windshields annually. And yet, pigeons seem to never hit a single telephone pole, cable, flag post, or anything else a cityscape can throw at them. How can this be? A new study of mid-flight behavior has the answer.

Published in the journal Proceedings of the National Academy of Sciences (PNAS), a new study details how pigeons instinctively know when to switch between safe or efficient flight.

What do I mean by that? Researchers David Williams and Andre Biewener at Harvard University were able to get some exceptional footage of pigeons dodging random obstacles after they trained four of urban life's infamous flying rats to fly back and forth across a flight corridor. After the pigeons made this trek an everyday thing, the researchers introduced obstacles into their paths.

What they found was that pigeons take one of two approaches to avoid slamming their delicate wings into tight spaces.

They can choose the safest approach, which is to fold their wings completely against their bodies - temporarily losing altitude in the process; or they could chose to do a so-called "wing pause" where they simply don't lower their wings from over their head mid-flight. This second approach is also more energy efficient, as it allows the pigeon to immediately resume flapping once the obstacle is cleared.

It was thought that perhaps which way the birds chose was simply based on the timing of their flaps, but after running several experiments with wider or smaller gaps between or around obstacles, Williams and Biewener found that pigeons are actually actively making the decision.

"The choice between these two postures seems mediated by an element of caution or uncertainly," they wrote in the study. "The efficient flight strategy (wing pause) is chosen where gaps are wider and there is less chance of a collision occurring."

Otherwise, when there is too much risk of breaking a wing, the pigeons seem to be willing to make the extra effort, explaining why few-to-no collisions are ever seen.

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