Researchers have documented an unexpected mechanical courtship signal in scissor-tailed nightjars in northern Argentina. The study, published in the Journal of Avian Biology, was led by Christopher Clark of UC Riverside with Juan Ignacio Areta of CONICET and used high-speed infrared cameras to record the behaviour.
Male nightjars, which have long forked tails and hunt at night for moths and beetles, perform dramatic displays that include a sharp snapping sound long reported by observers. The team filmed males striking the wrist joints of their wings together during predawn hours, often in darkness near the full moon and commonly between 3 and 4 AM when ambient noise was low. Clark noted they used infrared light the birds could not see so the work did not affect behaviour.
Footage showed the snapping is non-vocal: the birds physically collide the radius bones in their wings, producing a clap-like sound. The researchers examined museum specimens for special wrist structures but found no obvious anatomical modifications; Clark compared this to how humans can clap loudly without special adaptations.
The paper places the finding in a wider context: similar non-vocal displays exist in a few other birds but their mechanics are poorly understood. Clark’s lab is investigating whether some wing-generated noises might create tiny shock waves like those from fast metal collisions. The study also recorded another unusual sound during aerial chases, whose source remains unknown.
Difficult words
- mechanical — relating to physical movement or parts
- courtship — behaviour animals use to attract mates
- infrared — light with wavelengths longer than visible
- predawn — time just before sunrise, early morning
- ambient — present around a place, surrounding
- non-vocal — produced without using the voice
- collide — to hit something with force
- anatomical — related to the structure of a body
- specimen — an example individual kept for studyspecimens
- shock wave — a sudden pressure wave after a fast impactshock waves
Tip: hover, focus or tap highlighted words in the article to see quick definitions while you read or listen.
Discussion questions
- How does using high-speed infrared cameras help researchers study nocturnal birds without changing their behaviour?
- Why might non-vocal mechanical signals evolve in birds instead of vocal calls? Give two possible advantages.
- What experiments or observations would you propose to identify the source of the unusual sound recorded during aerial chases?
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