High-speed cameras show how small birds continue to flap their wings while flying sideways.
Introduction
Hummingbirds are acrobatic performers, twisting their wings in ways that allow them to fly backward and upside down, unlike any other bird. New high-speed video clips now reveal how hummingbirds can also slip through gaps narrower than their wingspan.
Sideways Flight of Hummingbirds
Anna’s hummingbirds fly sideways to pass through very small holes that cannot accommodate their rigid wings, researchers report in a study published on November 9 in the Journal of Experimental Biology. To avoid crashing into the sides of the gap, the birds also oscillate their wings while maneuvering through the tight space, instead of using their full range of motion for each wingbeat. After successfully navigating the obstacle several times, the birds change their approach, compressing their wings against their bodies and darting through the holes like a bullet.
Impact of Discovery on Technology
These findings could help engineers develop aerial vehicles or robots suitable for navigating narrow and complex spaces. Hummingbirds are among the best flyers in nature and possess a remarkable ability to remember their spatial environments, according to Bo Cheng, a mechanical engineer at the University of Pennsylvania who was not involved in the study. However, “the state of the art in primitive aircraft has not really reached the level of hummingbird flight yet,” as hummingbirds have precise control over their flight thanks to their rapid wing beats – about 40 beats per second for Anna’s hummingbird – and the engineering field needs to catch up with these developments.
How Hummingbirds Deal with Obstacles and Tight Spaces
Due to the rigidity of hummingbird wings, researcher Mark Badger wondered how the birds navigate obstacles and tight spaces. While studying as a graduate student at the University of California, Berkeley, he observed the small birds drinking nectar from feeders. At times, the birds would chase each other through the branches of a nearby shrub yet emerge unscathed. He said, “That got me thinking, how in the world do they do that?”
He and his colleagues captured four male wild Anna’s hummingbirds and trained them to fly between two feeders in an enclosed flight arena. Once the birds adjusted to the setup, the team placed barriers with openings ranging from 6 to 12 centimeters in diameter, equivalent to half or full wingspan of the hummingbirds.
To the human eye, the hummingbirds appear to fly from feeder to feeder on the computer screens monitoring the arena, according to Badger, who now works as an engineer at Aescape, a therapeutic robotics company in New York City. But the high-speed cameras positioned at the side and below the gap showed that the birds first used sideways flight to move through the narrow openings. Then each bird transitioned to diving through the gap.
Robert Dudley, a physiologist at the University of California, Berkeley, said, “There was a big surprise in seeing the sideways motion,” as he had assumed that hummingbirds would only use the ballistic approach, flattening their wings against their bodies as many songbirds do. He added, “But the slow motion and then moving sideways without losing altitude was a new behavior that had never been seen before.”
It is unclear whether the hummingbirds learned the navigation techniques in the lab or brought a set of innate strategies with them, according to Badger. But all four birds began by flying sideways and transitioned to the bullet technique, suggesting that the same tactics could be used in the wild.
It is also unknown why hummingbirds might use either technique. Sideways flight may provide flexibility to reverse course around obstacles where predators such as cats might be lurking, according to Badger. However, due to continuous wing oscillation, feathers could also collide with objects and break. Badger said, “The story I tell myself is that once they get a sense of what’s on the other side and have an idea of their surroundings, they switch to this bullet technique to avoid consequences.”
Do
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A version of this article appears in the December 16, 2023 issue of Science News.
References:
M.A. Badger et al. Sideways maneuvers enable narrow aperture negotiation by free-flying hummingbirds. Journal of Experimental Biology. Published online November 9, 2023. doi: 10.1242/jeb.245643.
Irene Garcia de Jesus is a writer for Science News. She holds a Ph.D. in microbiology from the University of Washington and a master’s degree in science communication from the University of California, Santa Cruz.
Source: https://www.sciencenews.org/article/hummingbirds-fly-spaces-narrow-wings
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