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This is 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 Starwing, there has been this fact that birds produce sounds with wings and tails or flight feathers.

So there are species of mannequins that do these sounds and there's hummingbirds that do the sounds.

Valentina Gomez-Bamun is an evolutionary biologist and ornithologist at the Field Museum in Chicago.

She and her team have now observed that non-vocal 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 bird's 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.

So basically what we think is that because of loss of migration, pressures for flight may influence the shape of the individual feathers to the point where the sound

quality changes as well. The details are in the journal Integrative and Comparative biology.

Gomez-Bamon says they're still not certain what role the sounds play in day-to-day fly-at-your-life,

if the birds do indeed even pay attention to them.

But she suspects the sounds may have some cultural importance to the

birds, in which case she says the communication differences between the migratory

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