By Mark Brown, Wired UK

A Yale University zoologist has used a laser vibrometer and high speed videos from a wind tunnel to work out how the hummingbird makes its famous hum, and found that the males of each species have their own signature sound.

The male hummingbird produces a high-pitched fluttering sound during its elaborate courtship ritual. The bird will fly five to 40 meters into the air, before quickly dive-bombing past a perched female. At the lowest point, he rapidly spreads and closes his tail feathers to produce the hum.

Clark used a Scanning Laser Doppler Vibrometer — an instrument that is used to measure the vibrations of a surface — to measure the fluttering feathers, and studied the different feathers shapes and movements by viewing high speed videos of the tail feathers in a wind tunnel.

The data reveals that the feather spreading causes the features of the tail to be exposed to air, which causes them to flutter and generate noise. This also causes neighboring feathers to flutter, amplifying the sound — two feathers fluttering in unison can produce a sound about 12 decibels louder than two fluttering independently.

These different frequencies, volumes and sounds give the males of each hummingbird species their own signature noise. Other factors, such as the size, shape, mass and stiffness of the feathers also help determine the tone of each species’ sound. “The sounds that hummingbird feathers can make are more varied than I expected,” said Yale University’s Christopher Clark in a press release.

Clark hypothesizes that the volume of the sound made by the male hummingbird is impressive to females, who see the noise as an indicator of the male’s flying prowess. The loudest males would thereby gain a selective advantage and be favored by evolution — leading to the sounds we hear today.

Video: Christopher Clark/NSF

Image: Anand Varma/www.varmaphoto.com

Source: Wired.co.uk

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