This is Scientific American's 60-second Science, I'm Christopher Intagliata.Charles Darwin is most famous for his finches, from whose beaks he gleaned the idea that a single species might radiate into many.But he studied other attributes of birds, too―like the rhythmic sounds some species made during courtship by fluttering, shaking or rattling their feathers together."Since Darwin, there's been this fact that birds produce sounds with wings and tails or flight feathers.So there's species of manakins that do this sound; there's hummingbirds that do this sound."Valentina Gómez-Bahamón is an evolutionary biologist and ornithologist at the Field Museum in Chicago.She and her team have now observed that nonvocal-sound-production phenomenon in another type of bird: the fork-tailed flycatcher.The researchers studied two groups of the birds in South America―and recorded the birds making these fluttering sounds with their wings during morning courtship rituals...... and in combat between males.One of the two flycatcher subspecies is migratory. The other stays put.And by carefully measuring the birds' feathers, the research team found that the migratory birds had longer, thinner feathers―presumably for some aerodynamic advantage.But that altered feather shape also meant the birds' fluttering produced a different frequency.Compare the migratory birds' flutter...... to the stationary birds'.
