Hummingbird Feather Songs Set Females All Aflutter

By Mimi Nguyen Ly
September 8, 2011

Hummingbirds are well known for their hovering antics and being able to fly backwards. But these little guys have another idiosyncrasy—in some species, the males make loud noises with their tail feathers to attract females.

A study published in Science on Sept. 9 explains the source of these courtship sounds, not usually heard during normal flight, which are due to "aeroelastic flutter."

In a typical courting ritual, the male flies 5 to 40 meters up in the air and nose-dives past a potential mate. At the lowest point of the maneuver, he quickly spreads and closes his tail feathers, generating the unique fluttering sounds.

Christopher Clark of Yale University and colleagues analyzed these sounds using a Scanning Laser Doppler Vibrometer to quantify the feathers’ vibrations. They also studied high-speed videos showing the tail feathers of 14 different species in a wind tunnel.

The team determined that multiple factors are at play, including the size, shape, and stiffness of tail plumage. And the faster the dive, the louder the sounds.

“The sounds that hummingbird feathers can make are more varied than I expected,” says Clark in a press release.

Each hummingbird species possesses a signature sound or feather song. The researchers found that various interactions among the feathers generate fluttering frequencies that blend into a distinct tone and timbre.

An example of such a synergy occurs when one feather causes an adjacent one to vibrate in the same way and produce a louder sound, like a vibrating tuning fork influences a nearby fork to hum in the same frequency.

"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,"says William Zamer, program director at the National Science Foundation, in the release.

Along with diving stunts, males also display their wings and can produce sounds from other feathers on their bodies.

Source: The Epoch Times.
Link: http://www.theepochtimes.com/n2/science/hummingbird-feather-songs-set-females-all-aflutter-61352.html.