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Hummingbirds adjust their wings to fly through very tiny spaces

In the intricate dance of the forest, where every gap and leaf presents a potential barrier, the hummingbird performs with a grace and skill that defy the limitations of its rigid wings.

Unlike other birds that bend their wings to navigate the dense foliage, hummingbirds have devised a remarkable set of maneuvers to traverse the tightest of spaces. Researchers at the University of California, Berkeley have uncovered the secrets of these extraordinary feats.

Hummingbird wings navigate tight spaces

The study reveals that hummingbirds employ two distinct strategies when faced with narrow passageways in their leafy realms. When confronting slits too slim for their wingspan, these avian acrobats sidestep through. Incredibly, they are able to maintain their elevation with continuous flaps.

For smaller openings or familiar routes, they adopt a more aerodynamic pose. This strategy involves tucking in their wings and gliding through before resuming their flapping.

How to study hummingbird wings

The amazing research is surprising in its revelation of the hummingbird’s lateral motion and intricate wing adjustments. It was led by Robert Dudley, a professor of integrative biology at UC Berkeley.

“For us, going into the experiments, the tuck and glide would have been the default. How else could they get through?” said Dudley. “This concept of sideways motion with a total mix-up of the wing kinematics is quite amazing — it’s a novel and unexpected method of aperture transit. They’re changing the amplitude of the wing beats so that they’re not dropping vertically when they do the sideways scooch.”

Dudley’s team included Marc Badger, who completed his Ph.D. at UC Berkeley. They observed that the birds alter their wingbeat amplitude to avoid vertical drops during these maneuvers. The sideways scooch, in particular, might offer the birds a better chance to evaluate and avoid obstacles, which could reduce collision risks.

“Learning more about how animals negotiate obstacles and other ‘building-blocks’ of the environment, such as wind gusts or turbulent regions, can improve our overall understanding of animal locomotion in complex environments,” noted first author Badger. “We still don’t know very much about how flight through clutter might be limited by geometric, aerodynamic, sensory, metabolic or structural processes. Even behavioral limitations could arise from longer-term effects, such as wear and tear on the body, as hinted at by the shift in aperture negotiation technique we observed in our study.”

Hummingbird obstacle course

Other members of the team included UC Berkeley students Kathryn McClain, Ashley Smiley, and Jessica Ye. They ingeniously trained hummingbirds to navigate through variable-sized apertures using high-speed cameras and a computer program developed by Badger.

They discovered that the birds hover momentarily to assess an aperture before engaging in their unique transit methods. Video of their experiment can be see here.

“We set up a two-sided flight arena and wondered how to train birds to fly through a 16-square- centimeter gap in the partition separating the two sides,” Badger said, noting that the hummingbirds have a wingspan of about 12 centimeters (4 3/4 inches). “Then, Kathryn had the amazing idea to use alternating rewards.”

How the study was conducted

The research team’s innovative approach to studying these birds involved alternating rewards with flower-shaped feeders. This compelled the hummingbirds to repeatedly pass through the testing apertures. This method provided a clear view of how hummingbirds manage to maintain lift and thrust even with asymmetrical wing movements.

“The thing is, they have to still maintain weight support, which is derived from both wings, and then control the horizontal thrust, which is pushing it forward. And they’re doing this with the right and left wing doing very peculiar things,” Dudley said. “Once again, this is just one more example of how, when pushed in some experimental situation, we can elicit control features that we don’t see in just a standard hovering hummingbird.”

The experiment also demonstrated the birds’ capability to adapt their strategies. The faster ‘ballistic buzz-through’ approach was employed more frequently as the birds grew accustomed to the test setup. Yet, in the face of the smallest gaps, the hummingbirds resorted to the ‘tuck and glide’ move. This adaptation indicates a versatile and adaptive approach to obstacle navigation.

“They seem to do the faster method, the ballistic buzz-through, when they get more acquainted with the system,” Dudley said.

The findings also highlight the birds’ resilience. Only 8% of the hummingbirds experienced wing clipping, and even then, they quickly recovered and continued their flight.

“The ability to pick among several obstacle negotiation strategies can allow animals to reliably squeeze through tight gaps and recover from mistakes,” Badger noted.

Real world applications through biomimicry

The implications of these findings stretch far beyond biological curiosity. Understanding how birds like hummingbirds navigate cluttered spaces could inform the design of drones capable of better maneuvering in complex environments.

Badger suggests that the flapping wings and sensory prowess of birds might offer insights that could revolutionize how drones interact with their surroundings, especially in turbulent or obstructed areas.

“Current remote control quadrotors can outperform most birds in open space across most metrics of performance. So is there any reason to continue learning from nature?” said Badger. “Yes. I think it’s in how animals interact with complex environments. If we put a bird’s brain inside a quadrotor, would the cyborg bird or a normal bird be better at flying through a dense forest in the wind? There may be many sensory and physical advantages to flapping wings in turbulent or cluttered environments.”

Next steps for avian flight research

Dudley’s team aims to delve deeper into the mystery of avian navigation by testing the birds with a series of varied apertures, seeking to understand how they address multiple obstacles in succession. Their research stands as a testament to the hummingbird’s ingenuity, revealing the intricate strategies these tiny creatures employ to thrive in their complex habitats.

The full study was published in the Journal of Experimental Biology.

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