Life

CLUB-shaped feathers are no good for flying, but when it comes to courting they can be music to a mate's ears.

The irregular structure of these heavy, specialised feathers is responsible for creating the club-winged manakin's unique high-pitched courtship song, say Kimberly Bostwick and colleagues at Cornell University in Ithaca, New York. The songbird (Machaeropterus deliciosus) uses these feathers for stridulation, a rubbing mechanism commonly used by insects such as crickets.

One feather on each wing has seven ridges along its central vane. The stiff, curved tip of an adjacent feather strikes the ridges every time the bird raises it wings over its back and shakes its feathers. The repeated striking causes adjacent clubbed feathers to vibrate at high speed.

The mechanism was first proposed after viewing slow-motion footage of male courting behaviour. To find out whether the vibrations produced the manakin's mating song, Bostwick's team shook the birds' seven club-shaped secondary feathers at varying rates. Vibrating the sixth and seventh feathers together at 1500 cycles per second produced the correct tone. The other feathers did not produce the noise, suggesting they are instead responsible for radiating the sound (Proceedings of the Royal Society B, DOI: 10.1098/rspb.2009.1576).

Although many insects do this, manakins are unique among vertebrates in using stridulation, says Bostwick.

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