WORLD SCIENCE

"Long before it's in the papers"
December 20, 2005

July 28, 2005
Courtesy Cornell University
and World Science staff

Hummingbirds and rattlesnakes move parts of their bodies at amazing speeds. But male club-winged manakins—colorful, sparrow-sized South American birds—have them both beat, researchers say. 

The male club-winged manakin, seen here from below, rubs specialized wing feathers behind its back to produce a violin-like serenade for mates, researchers say. (© Science)

The manakins vibrate their wings at more than 100 cycles per second, twice the speed of hummingbirds. 

The bird uses this unprecedented feat not for fight or flight, but to impress females with its violinlike hum. 

Similar to how a cricket chirps by rubbing together sound-making apparatus in its wings, male club-winged manakins (Machaeropterus deliciosus ) use specially adapted feathers in each wing to make a tone, according to a Cornell University ornithologist.

The findings are published in the July 29 issue of the research journal Science. 

The sound and how the bird produces it are unique among vertebrates, the authors said.

“Essentially an instrument has evolved in this species, in this case a refined instrument,” said Cornell University’s Kimberly Bostwick, the lead author.

The club-winged manakin is found only in a strip of threatened cloud forest on the western slopes of the Andes Mountains along the extreme northwest corner of Ecuador extending into Colombia.

It has adapted its wings in this way, Bostwick said, due to what biologists call sexual selection, the process by which evolution favors animals who are best able to attract mates.

The sound makes the male more attractive to females, Bostwick explained. 

“In general, if an adaptation is really weird and out there, it is produced by sexual selection,” said Bostwick, pointing out that peacock wings are another example of an adaptation due to sexual selection. 

Darwin mentioned the club-winged manakin in “The Descent of Man,” his treatise on sexual selection and how characteristics that attract the opposite sex are passed down to the next generation.

Darwin was fascinated that birds have vocal chords and sing, but he was particularly struck that some birds make noise with their bodies, Bostwick said. Although Darwin’s book includes illustrations of the club-winged manakin’s unusual feathers, Darwin did not know about the sound they produce or how it is generated. 

Since the bird makes the noise by moving its wings at a blinding speed, that finding had to wait for technology that has only been developed in the last few years, said Bostwick, noting that this study marks the first explanation of how these birds generate the tone. 

To study the bird, Bostwick used not conventional video cameras, but a special digital video camera designed to capture up to 1,000 frames a second for high-speed industrial processes. 

High-speed video recordings, played back in slow motion, revealed that to attract a mate, the male leans forward, raises its wings behind its back and flips them to make the hum. In humans, the move would be analogous to leaning forward and touching elbows and pinkies behind one’s back. 

Bostwick determined that special inner feathers rub together to make the sound. Each wing has one feather with a pick, or a small blade, and an adjacent feather with ridges and enlarged and hollow shafts. 

While perched, the bird hits the wings together quickly, she explained. Each wing creates its own violinlike hum as the pick feather rubs against the adjacent ridged feather. 

Manakins are lek-breeding birds, meaning that the males compete to mate, while the females raise the young. Since the males do not couple to raise young, a single male could inseminate all the local females. Therefore, competition for females among lek-breeding birds creates strong pressures for sexual selection, Bostwick said.

While other birds make wing sounds — including other types of manakins, grouse, pheasants, hummingbirds and birds of paradise — and many of the 40 kinds of manakins have developed wing buzzes, snaps and hums, none of these sexually selected adaptations are as extreme as the club-winged manakin, Bostwick said.

Send us a comment on this story, or send it to a friend

WORLD SCIENCE

WORLD SCIENCE