AINEWS
Scissor-tailed nightjars court with a bone-on-bone snap of their wings
Researchers in Argentina captured high speed infrared video of male Hydropsalis torquata clacking the wrist bones in their wings during nighttime mating displays.
Researchers in Argentina captured high speed infrared video of male Hydropsalis torquata clacking the wrist bones in their wings during nighttime mating displays.
A sharp crack splits the night air in the Andean foothills. It is not a falling branch or a startled animal making the sound. It is a bird: the male scissor-tailed nightjar, snapping the bones of his own wings together to court a female in the dark.
The behavior is described in the Journal of Avian Biology's May 2026 issue, which documents how male Hydropsalis torquata, a nocturnal insect-eater related to hummingbirds and swifts, has evolved a mating signal that bypasses the voice box entirely. When a male swings both wings behind his back in a violent collision, the wrist bones just below the wing's last bend strike each other with enough force to produce an audible pop. The researchers suspect the bone-on-bone impact sets the bones themselves vibrating, generating the sudden, staccato crack that carries through the forest.
Juan Ignacio Areta of the Instituto de Bio y Geociencias del Noroeste Argentino in Salta and Christopher Clark of UC Riverside captured the behavior by filming the birds at night along a forest road near Salta, Argentina, in late 2022. They used high-speed infrared cameras and synchronized the footage to recorded audio, allowing the team to see, frame by frame, exactly which body parts produced each snap, according to Jake Buehler's reporting in Science News.
Males perform the snap while hopping on the ground and swinging their wings behind their backs, sometimes during flight and occasionally while mating with a female. The same crack shows up when males chase intruders away from a territory. The signal's specific meaning to other nightjars remains unknown; the researchers can only confirm that the sound accompanies courtship, mating, and territorial encounters.
Scissor-tailed nightjars are unusual among nightjars for their exceptionally long, paired tail feathers. In a broader sense, the species joins a small percussion band of birds that produce non-vocal mating sounds. Male Siberian grouse strike their wing feathers together, male riflebirds scrape their bills across their wings, and some manakins have been documented snapping their wrist bones, the only other birds known to use the same skeletal mechanism. Areta, quoted in Science News, frames the nightjar as a new member of a small, strange club of avian instrumentalists.
What the snap actually communicates to a female scissor-tailed nightjar, beyond announcing a male's presence and intent, is the next question the researchers hope to answer. Areta and Clark plan to compare the snaps of courting males with those used in territorial fights to see whether the sounds vary in ways the birds themselves can read.