To see a manakin in action is to encounter a spectacular song and dance act in the middle of a tropical forest. About half of the 40 known species make music by moving their body parts. And in the flush of courtship, males execute maneuvers with names like the dart, the about-face, the upright, and the backward slide (which looks exactly like a Michael Jackson moonwalk).
Charles Darwin sized up the manakin in The Descent of Man. In his 1871 account of the bird, he wrote: “The diversity of the sounds … and the diversity of the means for producing such sounds, are highly remarkable. We thus gain a high idea of their importance for sexual purposes.” But the mechanics of its music making have taken more than a century to uncover.
Just a handful of ornithologists study the club-winged manakin, which lives in Colombia and Ecuador. Probably none is more in tune with the bird than Kim Bostwick. It was Bostwick—first working with her Ph.D. adviser at Yale, Richard Prum, and then since 2002 as curator of birds and mammals at the Cornell University Museum of Vertebrates—who broke the code of the male club-winged manakin, a standout among manakins. It is the only species that uses its feathers to generate a tick, tick, ting in the hope of making a female swoon.
Scientists knew the wings were the source of the sound but didn’t know exactly how the process worked. To crack the conundrum, Bostwick recorded the bird’s movements on a video camera operating at a thousand frames per second, more than 30 times as fast as a standard camcorder. Viewing the video a few frames at a time led to a eureka moment: The bird was knocking its wings together 107 times a second. Examining the bird’s secondary feathers in the lab, Bostwick saw on each wing a specialized feather with seven separate ridges. The fifth feather rubs against the ridged feather in a plectrum-like action—in music terminology, that’s a plucking device, like a guitar pick—to reach a frequency of an astonishing 1,500 cycles per second (seven ridges, each plucked twice = 14, multiplied by 107 = 1,498). The result is a violin-like tone, somewhere between an F sharp and a G, more than two octaves above middle C. The world has nearly 10,000 species of avifauna, but no other creates sound this way—by scraping body parts together (although crickets do something similar).
Bone density appears to be critical. In a paper that will be published later this year, Bostwick and her colleagues describe how they conducted micro-CT scans of manakin wings and discovered that the wing bones are solid. Most birds have hollow bones, which lighten the load when aloft. The manakin’s bulky bones, Bostwick says, likely have evolved in order to support the knocking action of the large feathers. But how, she wants to know, does this three-and-a-half-inch bird haul around the extra weight when it flies? And how does it manage “the incredible energy cost and physics involved in using that wing”? These are the next manakin mysteries to solve.