Males of a South American forest bird make courtship music with built-in scrapers—just as insects do. This is the first example of a vertebrate producing sound in this manner, scientists report.
A male club-winged manakin in Ecuador creates a series of seductive “tick tick tings” by knocking together his wings over his back, says Kimberly Bostwick of Cornell University. A single knock makes the tick, and repeated, high-speed knocks make the ting. That ting requires that kinked wing feathers repeatedly slide over tiny washboard ridges on the feathers beside them when the wings come together.
Although crickets and other musical insects rasp a scraper over a ribbed surface, scientists had never before demonstrated such stridulation in a vertebrate, say Bostwick and Richard Prum of Yale University in the July 29 Science.
Plenty of birds make some kind of noise with their wings, says Bostwick, but most of these sounds are subtle. Yet the several-dozen species in the manakin family include about 20 that can knock their wings loudly enough to be heard meters away in the forest. “It’s a family of male show-offs,” says Bostwick.
In this noisy family, club-winged manakins (Machaeropterus deliciosus) stand out as the only ones to make a musical tone as well as percussive whacks. It’s taken Bostwick since 1997 to figure out how the birds ting.
In a recent expedition, she used a camera that caught at least 500 frames a second. At this speed, she documented how males maneuver their wings to clap over their backs but couldn’t explain the musical note. The tone required a vibration with a frequency at least 10 times as fast as that of the wing clapping she measured during the ting.
Bostwick found the answer when she experimented with unattached wing feathers. She could feel a kinked wing feather catch on ridges when it scraped against a neighboring feather’s shaft. On the bird, one knock sends the kinked feather back and forth over its neighbor’s multiple ridges, creating the high-frequency vibration, she says.
During breeding season, male manakins defend neighboring performance stages. When a cruising female lands on a male’s perch, he works his wings frenetically, backing toward her until he’s tick tick tinging a few inches from her face.
The remarkable wing adaptations “show the power of female choice,” says Bostwick.
Ornithologist Alan Brush of Mystic, Conn., says that the bird’s wing motions remind him of flight. “It’s a really good example in evolution of the use of one mechanism for another function,” he says.
But evolution brings trade-offs, according to Jose Tello of the American Museum of Natural History in New York. He points out that these manakins have unusually small vocal muscles and few calls.
