Hummingbirds Control Their Flight with a Newfound Mechanism

The Olympic gymnasts of birds are hummingbirds. They fly backwards and upside down, hover, and fly at high speeds. Flips are possible.

In the Proceedings of the Royal Society B, researchers report that hummingbirds employ multiple visual processing modes to govern different flying patterns. In instance, the scientists found a novel way hummingbirds fly forward.

Analysis of over 3,500 hummingbird flights in a 12-foot tube with a perch and food yielded the results.

Moving patterns on the tunnel walls altered the hummingbirds' optic flow—the perceived motion of their surroundings. Pattern velocity, an important visual cue, helps many animals modify their speed and posture.

Researchers expected hummingbirds to speed or slow in coordination with vertical stripes projected on the side walls if they were employing pattern velocity cues to control their forward flight speed.

Instead, “it seemed more the case that they have their own internal speedometer or internal gauge” for forward flight, says University of British Columbia comparative physiologist Vikram Baliga.

Anything that violated the hummingbirds' assumptions of how their surroundings should change slowed them down, even vertical stripes flowing toward the feeder

which the researchers expected to speed them up. When hovering or moving up or down, birds used projected patterns to control their motors.

According to research co-author Doug Altshuler, a University of British Columbia biologist who studies complicated locomotion, hummingbirds are agile because they can switch flight modes.

Hummingbird brains rapidly switch from visual to motor outputs. He continues, “You watch them fly through the forest, and they’re dodging trees and moving branches in the wind—and each other.”  

Birds foresee how their movement will alter landscape, which will be studied further. Engineers may improve drone technology by understanding that, says Penn State mechanical engineer Bo Cheng.

Can we create a mathematical model to anticipate optical flow? Cheng asks. Maybe “that could be very useful for drones.”

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