With hummingbirds’ unique side-to-side vibration, they pass through small openings

Most birds that fly through dense, leafy forests have a strategy for maneuvering through tight windows of vegetation, they bend their wings at the wrist or elbow and barrel.

But hummingbirds can’t bend their wing bones in flight, so how do they navigate the gaps between leaves and tangled branches?

A study published today Journal of Experimental Biology shows that hummingbirds have developed their own unique strategy, two of them in fact. These strategies have not been previously reported, probably because hummers maneuver too quickly to be seen by the human eye.

Because slit-like gaps are too narrow to accommodate their wingspan, they spin sideways through the slit, constantly flapping their wings to maintain altitude.

For smaller holes, if the birds are already familiar with what awaits them on the other side, they tuck their wings and palm, resuming flapping when it is clear.

“For us, going into testing, shut up and glide would be the default. How else could they get through?’ said Robert Dudley, a professor of integrative biology at the University of California, Berkeley and senior author of the paper. “This concept of lateral movement with a complete mess of wing kinematics is quite surprising as it is a new and unexpected method of gap crossing. They change the amplitude of their wing beats so that they don’t fall vertically when they do. next door”.

Using a slower lateral scooting technique can allow birds to better assess upcoming obstacles and voids, thereby reducing the likelihood of collisions.

“Learning more about how animals negotiate environmental obstacles and other ‘building blocks’ such as wind gusts or turbulent regions can improve our overall understanding of animal movement in complex environments,” said first author Mark Badger, who received the is his Ph. .D from UC Berkeley in 2016.

“We still don’t know much about how flight through turbulence can be driven by geometric, aerodynamic, sensory, metabolic or structural processes. Even behavioral limitations can result from longer-term effects such as wear and tear on the body. implied by the change in gap negotiation techniques we observed in our study.’

Understanding the strategies birds use to maneuver in cluttered environments could ultimately help engineers design drones that better navigate complex environments, he noted.

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

Obstacle course

To find out how, in this case, four Anna’s hummingbirds (Calypte anna) glide through small openings despite being unable to fold their wings, Badger and Dudley teamed up with UC Berkeley students Kathryn McClain, Ashley Smiley, and Jessica Yeh.

“We created a two-way flight arena and figured out how to train the birds to fly through a partition separating the two sides with a 16-square-centimeter gap,” Badger said, noting that hummingbirds have a wingspan of about 12 centimeters. 4 3/4 inches). “Then Catherine had the amazing idea of ​​using alternative rewards.”

The team placed flower-shaped feeders on either side of the partition containing a sip of sugar solution, but only remotely filled the feeders after the bird visited the opposite feeder. This encouraged the birds to continuously fly through the gap between the two feeders.

The researchers then varied the shape of the opening from oval to circular, varying in height, width and diameter from 12 cm to 6 cm, and filmed the birds’ maneuvers with high-speed cameras. Badger wrote a computer program to track the position of each bird’s beak and wingtips as it approached and passed through the opening.

They found that when the birds approached an opening, they often hovered briefly to assess it before moving to the side, reaching forward with one wing and sweeping the other back, flapping their wings to support their weight as they passed through the opening. Then they flapped their wings forward to continue on their way.

“The thing is, they still have to maintain the weight support that comes from the two wings and then control the horizontal thrust that propels it forward. And they do this with the right and left wings doing very strange things. said Dudley. “Once again, this is another example of how, when pushed in an experimental situation, we can induce control features that we don’t see in a normal hovering hummingbird.”

Alternatively, the birds swept back their wings and attached them to their bodies, first shooting through the beak like a bullet before sweeping the wings forward and flapping them once to safety.

“They seem to be doing the faster method, the ballistic hum, as they get more familiar with the system,” Dudley said.

Just by approaching the smallest openings with half a wingspan, the birds will automatically turn to the hutch and glide, even though they were unaware of the equipment.

The team pointed out that only about 8% of the birds clipped their wings while crossing the barrier, although one of them had a major crash. Even then, the bird recovered quickly before successfully attempting the maneuver again and continuing on its way.

“The ability to choose among obstacle negotiation strategies may allow animals to reliably squeeze through narrow gaps and recover from mistakes,” Badger noted.

Dudley hopes to conduct further experiments, perhaps with different opening sequences, to determine how the birds navigate multiple obstacles.