Hummingbirds Wired to Dodge High-Speed Collisions

The tiny, super-speedy fliers process visual information differently than other animals.

It's no secret that hummingbirds are masters of aerodynamics, zooming along at high speed (up to 30 miles per hour), changing course in an instant as the objects around them dictate.

It's how they manage to move like that -- exerting such precise control -- without experiencing dangerous collisions that has been a bit of a mystery to scientists.

Researchers from the University of British Columbia (UBC) set out to solve the mystery, and the solution may lie in how the tiny birds process visual information.

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To test the hummingbird's use of in-flight vision, the researchers set up a tunnel in a laboratory and projected various patterns on its sides. Then they trained cameras on the birds as they flew through the tunnel and reacted to the patterns. (Sugar water on one end of the tunnel and a feeder on the other kept the birds only too happy to make this back-and-forth journey.)

First the scientists projected patterns meant to mimic the way bees process distance when piloting through the air. They knew that bees use the speed of objects as they pass by in their field of vision in order to gauge object distance, much in the same way humans, when driving on the highway, observe more distant objects going by slowly while things close by -- say, a rest area -- zoom past.

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But the birds did not react to the imagery based upon speed. Instead, the scientists observed, they used object size in the vertical axis to figure out how far away objects were, when flying left or right -- bigger meant closer while smaller meant farther away. In the test, the birds steered toward smaller imagery and away from bigger patterns.

"When objects grow in size, it can indicate how much time there is until they collide, even without knowing the actual size of the object," said the study's lead author Roslyn Dakin, UBC postdoctoral fellow, in a statement. "Perhaps this strategy allows birds to more precisely avoid collisions over the very wide range of flight speeds they use."

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The team also found that hummingbirds gauged their altitude similarly to insects, based on vertical-axis movement. They changed their flight -- up or down -- based on whether the patterns were going up or down.

"Our results suggest that in natural settings, birds may avoid collisions by monitoring the vertical size, expansion, and relative position of obstacles," the team wrote, in a paper just published in the journal Proceedings of the National Academy of Sciences.

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