The display begins with a climb of 30 metres or more, followed by a dive over a perched female. At the base of the dive the male spreads his tail briefly, and a loud chirp is produced. Because the bird also sings, the sound's origin was ambiguous for decades.
Christopher Clark and colleagues resolved it experimentally. Removing or manipulating the outer tail feather eliminated or altered the sound, and placing isolated feathers in a wind tunnel at dive airspeeds reproduced it. The mechanism is aeroelastic flutter: airflow sets the feather vane vibrating at a frequency set by its shape and stiffness.
Speeds recorded during these dives are high relative to body length, and the deceleration at the bottom is substantial, figures often quoted without their context of a very small bird. The remaining questions concern function rather than mechanism: how females assess the sound, and whether the acoustic or the visual component of the dive matters more, are not settled.