Hummingbird feathers create 'symphony'

Male hummingbirds court females with showy acrobatic dives and loud songs created by their tail feathers.

Allen's hummingbird produces separate tones with its narrowed tail feathers. (Credit: Anand Varma)

MALE HUMMINGBIRDS HAVE a courtship ritual that makes them all a-flutter, according to new research that breaks down the aerodynamics of their tail-feather love songs. 

The birds perform dive-bomb flights that cause their feathers to vibrate; sounds are produced when flowing air hits the tail feathers, causing them to flutter like flags in a breeze. The faster the dive, the louder the sound - which may help attract females by indicating how athletic and talented at flying the males are.

This 'aerodynamic flutter' is bad news for aeroplanes, but it helps each species of hummingbird produce unique melodies, found researchers led by Dr Christopher Clark at Yale University in the USA.

Hummingbird's tail a musical lure

To test how the music is made, the researchers put 31 tail feathers from 14 species of hummingbird into a wind tunnel and measured the high-frequency vibrations that resulted. They discovered that different sizes and shapes of feathers vibrate at different frequencies, creating a whole musical "symphony" of sound.

Writing in this week's edition of the journal Science the researchers said: "Our work shows that the tail of male bee hummingbirds functions as an acoustic organ, and we suggest that sexual selection, through female choice for flutter-induced sounds, has driven the evolution of diversity in male tail morphology."

Hummingbirds can even produce two tones with their tail at the same time. "And it can get even more acoustically complicated," the experts write. "Some hummingbirds produce two tones with the tail and a third sound with their vocal chords - an example of 'three voiced' sound and a chorus [that] any female would find difficult to ignore."

Scroll down for a video of Chris Clark explaining the discovery.

Anna's Hummingbird produces sound with its tail. The outer tail-feather generates the sound, and the second-to-outer tail feather acts as an amplifier. (Credit: Chris Clark)