These hummingbirds aim their singing tail feathers to wow mates

There’s more subtlety than humans have realized in dropping out of the sky so fast your tail feathers sing.

Male Costa’s hummingbirds in western North America are masters of the tail-screaming courtship plunge. Acoustic cameras recorded these repeated stunts and revealed that, as the male whooshes down, he twists half of his tail sideways, says ornithologist Christopher J. Clark of the University of California, Riverside. That twist aims the prolonged feather whistle toward the female he’s swooping by, Clark and his colleague Emily Mistick of the University of British Colombia in Vancouver report April 12 in Current Biology.
The recordings, which use microphone arrays to localize a sound on video, shed light on another quirk of Calypte costae’s performance. While male hummingbirds of other species swoop over the female during courtship dives, the shimmery purple-faced Costa’s zoom by on the side.

Extra distance in the side flyby minimizes the Doppler effect on the feather sound. That effect may be familiar from the EEEEEEooooo of an ambulance’s siren that sounds high-pitched as the vehicle approaches and then seems to lower after it passes. Masking the Doppler effect could make it harder for a female to pick out the fastest divers, although researchers haven’t shown how these females perceive speed or whether it matters much to them.

The diving sounds, made from the flutter of the outermost tail feather, also seem similar to the males’ vocalizations, Clark says. So he wonders if females find something in both especially seductive.