a hummingbird drinking from a straw that is attached to a wall with a black/white spiral

Unlocking the Secrets Behind the Hummingbird's Frenzy

To our eyes, they often are a blur. But high-speed cameras show us what makes these birds perfect flying machines.

A captive Anna’s hummingbird feeds while hovering before an optical illusion in a reenactment of an experiment that illustrates just how heavily hummingbird flight depends on the bird’s visual perceptions. When this spiral rotates to create the illusion that the bird is moving forward, the bird shifts into “reverse gear”—and its beak slips out of the feeder. (Sources: Benny Goller and Doug Altshuler, University of British Columbia, Vancouver)
This story appears in the July 2017 issue of National Geographic magazine.

In pursuit of the world’s smallest bird, we’ve come to the backyard of a flamingo pink house in Palpite, Cuba. Ornithologist Christopher Clark has a car full of gear to unload: cameras, sound equipment, a sheer cube-shaped cage. Within minutes of arriving this May morning, Clark is spinning around in circles. He’s trying to follow the path of a bullet with wings as it whizzes from one clump of orange fire bush blossoms to the next. When the hummingbird pauses to draw sugary fuel from the flowers, his wings continue to beat a grayish blur too fast for the human eye to resolve.

Even by the Lilliputian standards of hummingbirds, Cuba’s bee hummingbird (Mellisuga helenae) is a midget—literally the smallest bird in the world. Its iridescent green body weighs a bit more than the average almond. Locally it’s known as zunzuncito—the little buzz-buzz, after the sound it makes—and is even smaller than its cousin the zunzun, or emerald hummingbird.

What this bird lacks in size, he makes up for in enthusiasm when he spots a visitor in his territory. She’s a comely female, contained by the sheer cage that Clark brought and has placed on a corrugated metal roof. If the male notices this female’s enclosure, it doesn’t dampen his ardor. He helicopters up from his perch on a branch, hovers in the air, and lets out a trill in her direction.

He climbs higher, until he’s a pinprick against the cloudy sky. Then, like a roller coaster that’s reached its apex, he pitches forward and whooshes toward the ground. In an instant the daredevil is doing it all over again: climb, dive, and swoop. These plunges last a mere second. Then he vanishes, and the only trace of his passage is the leaves trembling in his wake.

Though I stared intently at the courtship show, I did not see it.

Neither did Clark, but he did something better. He recorded the display with a high-speed camera that slices each second of it into 500 frames. After Clark downloads video of the dive—the first ever recorded of this species at that high camera speed—he shows the footage to me on his laptop, clicking through every hard-won frame. Only then do we see the breathtaking maneuvers that the hummingbird’s speed had concealed.

For the past eight years, Clark has traveled from the Arizona desert to the Ecuadorian rain forest to rural Cuba, recording hummingbird courtship displays. Back in his lab at the University of California, Riverside, the professor examines the videos for what they reveal about hummingbird flight. His findings could contribute to our understanding of animal flight in general and hummingbird mating systems in particular.

With their rocketing movements and jewel-like plumage, hummingbirds seem like a hybrid of flesh, feather, and fireworks. The wings of some species flap up to a hundred times per second. Their heart rate can exceed a thousand beats per minute, and they gulp nectar with a near-invisible flick of the tongue. In gardens or at backyard feeders, they’re the definition of fleeting beauty. So who could resist the temptation to slow their motion, to dissect their movements—to inhabit, even briefly, the hummingbird’s world?

Hummingbirds live exclusively in the Americas. From southern Alaska to Tierra del Fuego, there are about 340 recognized species. Of these, 27—including the seemingly ubiquitous ruby-throated hummingbird—have been sighted in the United States. The center of hummingbird diversity is in the northern Andes, where 290 species reside in lowland rain forests, mountaintop cloud forests, and every ecosystem in between. The smallest can weigh less than two grams. The largest, the giant hummingbird found in Peru and Chile, tips the scales at around 20 grams. You could send something that weight in the U.S. mail with a single first-class stamp.

World’s smallest birds is just one of several distinctions that hummingbird species claim. They’re the only birds that can hover in still air for 30 seconds or more. They’re the only birds with a “reverse gear”—that is, they can truly fly backward. And they’re the record holders for the fastest metabolic rate of any vertebrate on the planet: A 2013 University of Toronto study concluded that if hummingbirds were the size of an average human, they’d need to drink more than one 12-ounce can of soda for every minute they’re hovering, because they burn sugar so fast. Small wonder that these birds will wage aerial dogfights to control a prime patch of nectar-laden flowers.

The tongue that sips from those flowers is a specialized organ, nearly transparent, and made up of two tubes rolled up like sheets of cellophane. As the bird drinks, its tongue flicks about rapidly, and as English naturalist William Charles Linnaeus Martin noted in 1852, the liquid “disappears very fast, perhaps by capillary attraction.”

When Alejandro Rico-Guevara, a postdoctoral researcher at the University of California, Berkeley, made high-speed films of hummingbirds drinking from feeders and flowers, he found that their forked tongues are more like a catcher’s mitt than like rigid drinking straws. Each tube of the tongue unfurls to snatch the nectar in a hundredth of a second. Then the birds pump the liquid into their gullets by squeezing their beaks. What a 19th-century scientist could only guess at, a 21st-century camera showed in minute detail.

The first attempt to analyze hummingbird flight is believed to have occurred in Nazi Germany in the late 1930s. With support from the Reich Office for Educational Film, two German ornithologists secured a camera capable of recording 1,500 frames a second from a military research institute. With it, they filmed two South American hummingbird species at Zoo Berlin. “The regime was developing the first helicopters,” says Karl Schuchmann, former curator of birds at the Alexander Koenig Zoological Research Museum in Bonn. “They wanted to know how birds could hover on the spot.”

The images showed hummingbirds to be more like bees or flies than like other birds, in that they generate lift on both the downstroke and the upstroke of their wings. When the ornithologists published their paper in 1939, they compared hummingbirds to the German Focke-Wulf helicopter.

In the United States, Crawford Greenewalt had served science on the opposite side of the war effort: He was an engineer with the Manhattan Project, the U.S.-led program that produced the first nuclear weapons. A dozen years after the German ornithologists published, Greenewalt picked up the thread of their investigation. His wife, Margaretta, had become interested in bird-watching at their home in Delaware, and from her Greenewalt caught what he called “hummingbird fever.” His hummingbird photographs were first published in the November 1960 issue of National Geographic.

Dissatisfied with the high-speed motion picture cameras then available, Greenewalt built his own. He filmed the flight of hummingbirds inside a homemade wind tunnel, capturing them at speeds up to 27 miles an hour. As the birds accelerated from a hovering position, Greenewalt documented the plane of their wings tilting from horizontal to vertical, redirecting their thrust.

The new images were groundbreaking, but they didn’t solve the mystery of how hummingbirds can flap their wings as quickly as they do. Typically, the faster a muscle contracts, the less force it generates. So how do hummingbirds produce enough force to stay aloft?

In 2011 Tyson Hedrick and his colleagues jury-rigged a way to answer that question. A University of North Carolina at Chapel Hill researcher who specializes in animal biomechanics, Hedrick knew that hummingbird wings are different from those of their closest relatives, the swifts. Hummingbird arm bones are relatively smaller, and most of the wing is made up of the equivalent of hand bones. To get a penetrating view of the wing moving at top speed, Hedrick coupled a camera that shoots a thousand frames per second with an x-ray imaging system.

When Hedrick viewed the frames in sequence, infinitesimal movements of the wing bones merged into patterns, then continuous motion, and the wing’s operation could be seen. Rather than flapping with an up-and-down motion of the shoulder, Hedrick discovered, hummingbirds flap with a twist. This modification gives them what amounts to a “high gear,” so that a millimeter-length muscle movement is enough to drive their wings across a wide arc.

Once, high-speed cameras were ungainly contraptions, difficult to operate and lug into the field. Now they can fit in a large pocket and are as essential to hummingbird biologists as binoculars are. The sheer magnitude of information captured by these cameras can be hard to fathom. To put Clark’s 500-frames-per-second videos in perspective, consider this: At the typical frames-per-second rate of a theatrical movie—let’s say, the 1939 classic Gone With the Wind—500 frames is roughly what it took for Scarlett O’Hara to run down the staircase, tearfully plead, “Rhett, Rhett! If you go, where shall I go? What shall I do?” and for Rhett Butler to answer, “Frankly, my dear, I don’t give a damn,” walk out the door, and disappear into the fog.

By slowing down time, scientists learn more about what happens when biology brushes up against the laws of physics. “There’s stuff that you absolutely do not see with the naked eye,” Clark says. “Put a high-speed camera on it, and you’re like, ‘Holy cow! That’s what the bird’s doing?’ ”

When some species spread their tails during 60-mile-an-hour dives, he says, there’s a chirping sound—not from their vocal cords but from the fluttering of tail feathers as air rushes through. In courtship displays some hummingbird species almost double their wingbeat frequency; others flap with a single wing. And when the Anna’s hummingbird pulls up after a stunt, it is subjected to roughly nine times the force of gravity—enough that a human fighter pilot, even one wearing a specialized G suit, could pass out.

“Hummingbirds can do extraordinary things using the same building blocks found in ordinary birds,” says Doug Altshuler, a comparative physiologist at the University of British Columbia in Vancouver. So studying their lives can tell us a great deal about general principles of biology.

On a summer morning a red glow emerges from a doorway of a room that Altshuler has taken to calling Hell. His postdoctoral research colleague, Roslyn Dakin, greets us with a sheen of sweat on her forehead. The sauna-like atmosphere is generated by six LCD projectors beaming vertical stripes onto the walls of a tunnel that runs the length of the room. Inside that tunnel sits a male Anna’s hummingbird, watched from above by a panopticon of eight cameras.

Dakin is trying to figure out how the birds control their flight. Previous researchers theorized that flying animals have a cruise control circuit in their brains to balance movement across their field of vision. Bees do this. We do it too. When you’re driving along a wide, open highway, it feels natural to be going 70 miles an hour, but if you’re on a country road lined with trees, you’ll probably tap on the brakes.

Hummingbirds apparently operate under a different set of rules. In one of Dakin’s experiments, she has them flying through what’s essentially a visual treadmill. Surprisingly, they fly just as fast when vertical stripes are moving with their direction of motion as against it.

At the moment we’re watching a green dot jiggle around on the screen, an indicator that the hummingbird is sitting in the dark, doing practically nothing. Periodically, he lurches halfway down the tunnel but then boomerangs back to his perch. “It’s really annoying when they don’t do exactly what you want them to do,” she says—“which is most of the time.”

Dakin is convinced that hummingbirds have an instinctual wariness of larger shapes that helps them avoid collisions. Today she’s playing around with projecting more complicated patterns—including what looks, to my eyes, like Elvis Presley’s hair but is actually supposed to be a flower. To test this, she needs the bird to fly the length of the tunnel, which he is stubbornly refusing to do.

Suddenly he lets out a chirp, and I watch the green dot flit down the tunnel, pause at the feeder, and return. Dakin perks up; the day might not be a bust after all. She types a code for this data entry into her computer’s command prompt and hits enter. On the screen thousands of coordinates coalesce into a rainbow-colored piece of tinsel—a three-dimensional summary of 15 long seconds in the fast life of a hummingbird.

Your National Geographic Society membership helped fund this photographic coverage.
Once a nascent field biologist, Brendan Borrell is a freelance writer and a correspondent for Outside Magazine. Anand Varma is an award-winning photographer and a National Geographic Emerging Explorer.

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