An Ecuadorian mountain bird that “sings” with its wings has been a source of intrigue since Darwin’s time, but only now have scientists determined how the unique courtship song is generated.

The club-winged manakin’s singing ability lies in adapted wing feathers that act like tuning forks, producing a high-pitched, clear ring when vibrated at the correct frequency, according to new research.

“They’re just like any other small cute bird, and then they throw their wings over their back and make this sound that is totally out of this world,” said Kimberly Bostwick, who has been working on sound production in manakins since 1995.

Machaeropterus deliciosus beats its wings together more than 100 times a second — twice the rate of the humming bird. However, this feat alone cannot produce the bell-like “ting” that male manakins use during courtship routines and to warn other males off their territory.

Dr Bostwick solved the mystery after studying feathers from the manakin collection at the American Museum of Natural History in New York. She noticed that one feather on each wing had a peculiar feature: its central shaft had seven ridges. The feather next to the ridged feather had a stiff, curved tip.

She realised that each time a manakin beat its wings, the curved tip picked across the ridges of the neighbouring feather — seven times on the way in and seven on the way out or 14 times per wing-beat. So a bird beating its wings 107 times a second would produce a sound with a frequency of about 1,500 Hz.

The latest study, published today in the Royal Society journal Proceedings B, shows how this action creates a continuous ringing noise. By testing how the ridged feather responded when struck at different frequencies, Dr Bostwick and her colleagues showed that it resonated at exactly the frequency at which the pick runs its ridges — about 1,500Hz.

The mechanism is similar to that of crickets; the edges of the wings of male crickets have comb-like teeth and the chirping sound is created by running the top of one wing along the teeth at the bottom of the other wing.

While the technique is common among insects and arachnids, the manakin is the only vertebrate known to create sound in this way.

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