Anna's Hummingbird. Photo: Vinitha Fredenburgh/Audubon Photography Awards

Science

Hummingbirds Shake Their Tail Feathers to Generate High-Pitched Sounds

Some male hummingbirds have special feathers that audibly vibrate as they zoom around to impress females. Listen here.

To win over a lady love, some male hummingbirds perform an elaborate aerial dance. The show typically starts when he zips from side to side in front of the female, sometimes showing off his brightly colored throat feathers, called a gorget, and singing. Then the bird will rise high into the air—sometimes dozens of feet up—and throw himself into a steep, dare-devil dive. As he hurtles toward the ground, the hummingbird makes a distinctive, high-pitched sound.

Until recently, most scientists assumed that hummingbirds made this noise the way you would expect—with their vocal chords. But after reading an old scientific paper theorizing that the birds can create sound with their tails, Christopher Clark, a biologist at the University of California, Riverside, decided to test the theory.

By studying wild hummingbirds with and without their tail feathers, and also testing feathers in a wind tunnel, Clark figured out that when fast-moving air vibrates certain plumes, they flutter at an audible frequency. By fanning and furling their tail feathers as they dive, each species has composed its own unique dive soundtrack.

Since making his original discovery, Clark has studied more than 20 hummingbird species to better understand how and why males use their modified tail feathers to make sound. Because the birds dive and whistle primarily during the breeding season, Clark suspects the tail feathers evolved into instruments as a result of sexual selection. He says he’s even seen female hummingbirds sitting with eyes half-closed while the males dive, “like listening to a symphony, if you will.”  

Below are six North American species Clark has studied with the most distinctive tail sounds, which you can also listen to thanks to his recordings. Whether you want to close your eyes, though, is entirely up to you.

Anna’s Hummingbird

Breeding range: California and Oregon

Breeding season: Late fall through early summer

An Anna’s Hummingbird male begins his courtship ritual by hovering over a perched female and singing. The bird then ascends more than 100 feet into the air—and then dives sharply toward the ground, flapping his wings at first, gliding, then flapping again. As he pulls up through the bottom of the dive with wings spread, he momentarily experiences high G-forces, Clark says. At this point, the hummingbird rapidly opens and closes his tail. As air rushes over the bird’s two outermost tail feathers, it unleashes a loud, distinctive beep.

Anna’s Hummingbirds always dive facing the sun. Doing so emphasizes their pink gorgets and facial feathers through the entire dive. The result is “this magenta comet falling out of the sky that culminates in this explosive squeak,” Clark says.  

They also dive frequently: In many hummingbird species, males will perform repeatedly for a female, but Anna’s Hummingbirds take this to another level. In the wild, Clark says he has seen a male dive 40 times in a row.  

Costa’s Hummingbird

Breeding range: Southern California, Southern Utah, Southwestern Arizona, Northwestern Mexico

Breeding Season: Winter through late spring

Unlike other species, male Costa’s Hummingbirds don’t dive directly over their love interest, and instead will veer off to the left or right near the end of their plummet. As the courter does this, he half opens his tail and swivels the feathers 90 degrees. This action directs the sound generated by the outermost tail feathers in the direction of the female.   

This behavior stumps Clark. He had assumed that female hummingbirds prefer fast-diving males, and that they might be able to deduce speed from the change in pitch as the male swoops overhead. (They would do this the same way you can determine how quickly an ambulance is moving past with your eyes closed: The rise and then drop in the siren’s pitch gives a sense of the vehicle's speed.) But by diving off to the side, male hummingbirds flatten this pitch change, making it difficult to determine how fast they're moving by ear alone. Clark is still trying to unravel why exactly the birds behave this way, and what it says about female hummingbird preferences.

Calliope Hummingbird

Breeding range: Southwestern Canada, Northwestern United States

Breeding season: Spring and summer

When Calliope Hummingbirds dive, they fly only 40 or 50 feet up in the air before plummeting, and their feathers make a funny buzzing noise. “People have compared it to a fart or flatulence,” Clark says.  

They make this sound when their outermost tail feather flutters as the birds move at high speeds. Anna’s and Costa’s Hummingbirds also sound off using this outer feather, but unlike those species, the Calliope’s outer feather then strikes other tail feathers. It’s these collisions that generate the buzzing noise at the bottom of the dive, says Clark. As they descend, Calliope males also make a whistling trill that Clark thinks is a burst of vocal song. 

Broad-tailed Hummingbird

Breeding range: Western United States, Central Mexico

Breeding season: Summer

Broad-tailed Hummingbirds make a racket even before they start diving. As the hummingbirds pump their wings through the air, the tips of their outermost wing feathers vibrate to make a cricket-like sound, Clark says. Without looking, you can hear these birds go up, up, up for a dive. Once they reach the apex, the wing trill slows down and then gets faster and faster as the bird accelerates. At the bottom, the male abruptly spreads his tail several times to make a rapid-fire bz bz bzt sound right at the end.

Broad-tailed males make this sound with their second innermost tail feather. This feather has a notch that causes the end of the feather to vibrate rapidly, producing harmonics, which the human ear interpret as “buzzy” rather than pure tones, Clark says.  

Unlike Anna’s Hummingbirds, which show off their bright gorget and head feathers throughout the entire dive, Broad-tailed Hummingbirds’ gorgets appear only as a quick flash of pink right at the end.

Allen’s Hummingbird

Breeding range: Southern Oregon, coastal California

Breeding season: Winter through early summer

When Allen’s Hummingbirds dive, their tail feathers make a high-pitched trill, or “pure, bell-like sound,” as Clark describes it. In this species, the middle tail feather produces noise when air moves over the tail, and the second-from-the-outside feather acts like an amplifier, turning up the volume on the tail whistle.

In addition to a big, steep dive, Allen’s Hummingbirds also make a series of shallow dives back and forth over the female. During this aptly named pendulum display, the male’s feathers emit another distinct set of sounds. No close relatives of the Allen’s Hummingbird display the same behavior, says Clark, and he’s currently trying to figure out what genes are responsible for this unique additional step to the mating ritual.

Rufous Hummingbird

Breeding range: Southern Alaska, Western Canada, Pacific Northwestern U.S.  

Breeding season: Spring and summer  

When a male Rufous Hummingbird dives, his wings become a blur of rapid motion while his tail writhes up and down. This species uses both wing and tail feathers moving through the air at high speeds to make its distinctively raspy dive sound, Clark says.

If you watch a Rufous dive in slow motion, you can see him hastily spreading his tail open and shut while beating his wings out of sync. Like Broad-Tailed Hummingbirds, Rufous Hummingbirds create buzzy tail sounds thanks to a notch in their second-innermost tail feather that allows the tip to flutter quickly. At the end of the dive, the wings beat out a loud chu chu chu as the tips of the outermost wing feathers vibrate rapidly.

Sometimes, hummingbirds will interbreed with another species, producing hybrid birds that perform hybrid dives. This occasionally happens with Anna’s and Costa’s Hummingbirds, which overlap in Southern California. On the southern coast of Oregon, Allen’s and Rufous Hummingbirds breed together all the time, says Clark, forming a hybrid zone where you can hear every possible combination of buzzy Rufous and bell-like Allen’s Hummingbird dives.

All recordings courtesy of Chris Clark, University of California, Riverside.​

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