As they zip around in search of nectar, hummingbirds have no trouble navigating dense foliage and other tight spaces. This feat is especially impressive for hummers, because unlike other birds, they can’t bend their wings at the wrist and elbow to tuck them into their bodies.
Without that ability, scientists wondered how hummingbirds squeeze through such tiny gaps—but the speedy fliers move too quickly for the human eye to follow.
Now, thanks to high-speed cameras, researchers finally know how the little creatures manage their acrobatic feats. In a study published last week in the Journal of Experimental Biology, scientists suggest hummingbirds use two different strategies to fly through small spaces: In one, they approach the gap slowly, hover for a brief moment and fly through sideways. In the other, they approach quickly, pin their wings back and dart through without flapping—much like a bullet.
“This is a new insight into the amazing capacity of hummingbirds,” says Bret Tobalske, a biologist at the University of Montana who was not involved in the research, to Science News’ Erin Garcia de Jesús.
Hummingbirds have long fascinated scientists. About 340 species exist in the wild, from teeny-tiny bee hummingbirds—the world’s smallest bird—to fiery-throated hummingbirds with their rainbow hues. Hummers are the only birds that can truly hover, and they can fly in any direction they choose—upside down, backward, forward, up and down. Scientists think they’ve also co-evolved with flowers: Because of their adaptations, hummingbirds get nearly exclusive access to the nectar they need to survive, while flowers get a dedicated team of pollinators to help them reproduce.
Marc Badger, a biologist and engineer at the University of California, Berkeley, was watching hummingbirds flit around outside his window when he became fascinated by their ability to quickly and effortlessly navigate dense foliage.
“When a dominant male would come and chase an intruder away, that intruder would fly through a bush,” Badger, one of the study’s co-authors, tells New Scientist’s Matthew Sparkes. “And it’s sort of like, ‘Wow, how are they doing that?’ It looks like it literally just teleported to the other side of the bush.”
He brought this question back to the lab, where a team of researchers came up with an experiment for studying hummingbirds’ flight patterns. They built an enclosure with two separate compartments connected by a small hole. One was left empty, and in the other, they installed a hummingbird feeder that dispensed a sugary solution.
The team set up high-speed cameras that could capture footage of the birds at up to 500 frames per second. The cameras were also linked to a computer program that recorded the positioning of the birds’ wing tips and bills as they flew.
With the infrastructure complete, the researchers brought in four Anna’s hummingbirds (Calypte anna) with wingspans of around five inches. One by one, they placed the birds into the empty side of the enclosure and waited for them to fly through the hole to the other compartment for a reward.
Throughout the course of the experiment, the scientists made the hole progressively smaller, beginning at roughly the length of their wingspan and narrowing it to about half that size.
When they slowed down the footage, the scientists could clearly see the birds’ two different approaches to fitting through the small holes—flying sideways or darting through with tucked wings.
Before the experiment, researchers had a hunch that the hummingbirds would tuck their wings and shoot through like a rocket—so it made sense to them when that was confirmed. But the sideways flying method took them by surprise.
“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,” says study co-author Robert Dudley, also a biologist at the University of California, Berkeley, in a statement. “They’re changing the amplitude of the wing beats so that they’re not dropping vertically when they do the sideways scooch.”
They also noticed an interesting pattern: With the larger holes, the birds started off by flying sideways, but as they got more comfortable with their surroundings, they used the “bullet” method more often. When they encountered the smallest hole, however, they all tucked their wings and darted through right away.
From this, the scientists developed a theory around why the birds might switch between the two strategies. Slowing down and flying sideways likely allows the birds to study their environment and reduce the possibility of collisions—or unexpected encounters with a potential predator on the other side. But it also probably increases the chance that they accidentally smack their wings on the hole as they fly through. So, they suggest, once the hummingbirds become confident enough to dart instead, they switch over.
On top of adding to our limited understanding of hummingbirds, these learnings could someday help improve the design of drones and other flying robots, the researchers say. Drones with four rotors, called quadrotors, outperform birds in open spaces, per the statement. But in flying through complicated terrain, nature has the edge.
“It’s in how animals interact with complex environments,” Badger says in the statement. “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.”