Hummingbirds Sing with their Tail Feathers

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"Scientists Reveal How Hummingbirds Sing with Their Tail Feathers

September 10, 2011 12:21 PM EDT

The hummingbird, one of the smallest birds famous for its mid-air hovering, has its name derived from a hum it produces during the male hummingbird's courtship ritual.

The exact source of its high-pitched fluttering sound has been identified for the first time, detailed in a paper published in the journal Science on Friday.

Christopher Clark of Yale University found out that male hummingbirds make the sound with their tail feathers during their courtship ritual to attract female hummingbirds. The sound is produced by the air flowing past the tail feathers, making them flutter.

During its courtship ritual, a male hummingbird would climb into the air 5 to 40 meters and dive-bomb down past a female. At the lowest point of his dive, the male would swiftly spread and close his tail feathers, making the fluttering sound.

Clark and colleagues collected feathers from 14 species of bee hummingbirds, and examined their sound-producing ability using a Scanning Laser Doppler Vibrometer, an instrument that is used to measure the vibrations of a surface.

When the winds were as fast as the hummingbirds' dive speed, the feathers vibrated rhythmically, producing a shriek.

More than individual feather, multiple feathers placed side by side amplify the sound, produced a louder noise by interacting with one another. The fluttering of one feather cause a neighboring feather to flutter, just like how the vibrations of one tuning fork may cause another nearby tuning fork to similarly vibrate, said the scientists.

The volume of the flutter also increases when the flying speed becomes faster.

They also concluded that each species has a signature sound, determined by factors such as the size, shape, mass and stiffness of the hummingbird's feathers.

"The sounds that hummingbird feathers can make are more varied than I expected," said Clark.

To be chosen by a female hummingbirds as a mate, a male bird would demonstrate its fitness using the high volume of the fluttering produced by its tail feathers, Clark suggested.

"This work is an excellent example of the use of physical approaches to understand the function of biological structures, and it reveals aerodynamic--rather than vocalized--signaling during courtship," said William Zamer, who directs NSF's Ecological and Evolutionary Physiology program.

"It is significant that the diversity of feather structures in these hummingbirds may result from sexual selection." "