Nightjars Use Wing Claps for Courtship, Researchers Discover

Scissor-tailed nightjars in northern Argentina produce a sharp clapping sound with their wings during courtship, a behavior documented in detail for the first time. This discovery reveals a hidden aspect of avian communication, where sounds are made mechanically rather than vocally. The findings were published in the *Journal of Avian Biology*.

Researchers used high-speed infrared cameras to film male nightjars in the predawn hours. The footage showed the birds striking the wrist joints of their wings together. This action creates a distinct clap-like sound during courtship displays and copulation. The birds performed these displays in darkness, often between three and four AM, near the full moon.

Christopher Clark, a biologist at the University of California, Riverside, co-led the study. Juan Ignacio Areta of Argentina's National Scientific and Technical Research Council (CONICET) also contributed to the research. The team confirmed that the snapping noise is not vocal. It results from the physical collision of the radius bones in the birds' wings.

Nightjars are nocturnal birds related to hummingbirds. Their mottled brown feathers provide camouflage. Their large eyes help them hunt insects in low light. Male nightjars have long, forked tails that spread during courtship. Scientists examined museum specimens but found no obvious anatomical modifications in the nightjars' wrists to facilitate the clapping sound. This suggests specialized structures may not be necessary for this behavior.

The study highlights how animals use mechanical sounds to communicate. Researchers are investigating whether these wing snaps can convey nuanced meanings, similar to vocalizations. Clark's laboratory studies the physics of unusual animal sounds to understand their evolution and the information they transmit. The research team also observed another unusual sound during aerial chases, the source of which remains unknown.