When male hummingbirds perform valiant dives in front of females, they are actually enticing them with high-frequency vibrations produced by their tail feathers, a new study reports.

The vibrations are audible, precise and separate from the humming of the wings that gives the birds their name.

Females may be making use of these vibrations to select mates, said the study's lead author, Christopher Clark, an expert on biomechanics at Yale.

Dr. Clark and his colleagues from Yale and the University of California, Berkeley, report their findings in the current issue of the journal Science. "The sounds of each species are fairly distinctive and fairly unique," he said. "It clearly evolved as a communication signal."

The researchers studied 31 tail feathers from 14 species of hummingbirds. They placed the feathers in a wind tunnel and used a Doppler vibrometer to measure the vibrations.

A light breeze produced no vibrations. But a higher velocity, simulating the wind speed generated when male birds are diving, touched off the sounds.

The researchers learned that feathers of different shapes and sizes resulted in different frequencies with different harmonic structures.

"It was different in different birds," Dr. Clark said. "In some cases it's just one tail feather vibrating, in some it is two hitting each other, and in some all the tail feathers are involved."

In one species, known as Anna's hummingbird, the vibrations could be heard more than 160 yards away. There are also slight variations among individual birds within a species. It is possible, Dr. Clark said, that females can detect how small differences in feather mass and shape change the sounds produced.

First Published: September 13, 2011, 4:00 a.m.