Sharp cracks split the nighttime air above the Andean foothills — sudden, percussive, nothing like the rustle of leaves or the snap of a branch underfoot. In forests where silence is the expected rule, something is deliberately breaking it. Not a predator. Not a human.
Most nocturnal animals go out of their way to stay quiet. What researchers heard here was the opposite: a creature making loud, abrupt sounds on purpose, night after night.
A bird that breaks the silence on purpose
The bird responsible is the scissor-tailed nightjar (Hydropsalis torquata), a nocturnal, insect-eating species related to hummingbirds and swifts. Males carry an immediately recognizable feature: exceptionally long, paired tail feathers that trail behind them in flight. By most measures, they are creatures built for the dark.
What made them puzzling was the noise. Males were already known to produce explosive cracking sounds at night — a mating signal directed at nearby females — but how they produced those sounds remained a mystery. Juan Ignacio Areta, an evolutionary naturalist at Instituto de Bio y Geociencias del Noroeste Argentino in Salta, Argentina, framed the contradiction directly: “Many nocturnal animals are well known for being extremely silent, such as the ‘silent’ flight of owls. We wanted to learn how it was possible for a nocturnal animal to make these loud sounds.” That question sent researchers into the field.
Filming in the dark: how researchers cracked the case
In late 2022, Areta and Christopher Clark — a behavioral ecologist at the University of California, Riverside — set up along a forest road near Salta, Argentina. Their goal was to catch the nightjars in the act without disturbing them. High-speed infrared cameras filmed covertly while simultaneously recording the sounds the birds produced.
The footage was revealing. Males would hop off the ground and swing their wings sharply together behind their backs, producing a loud clack on impact. The behavior was not confined to one context — males also snapped during flight and while mating. Whatever was driving it, this was not a single isolated display. It was woven through multiple moments of the bird’s nighttime activity.
Bones, not feathers: pinpointing the snap
The footage answered something that observation alone could not. Researchers confirmed the sound did not come from feathers slapping together. It originated from the wrist bones colliding just below the last bend in the wing.
Areta and Clark propose that the bones vibrate from the force of the collision, generating the sharp, percussive crack. The distinction matters because feathers are soft and flexible — they can produce sound, but not typically one this abrupt or loud. Bones are rigid, and a forceful collision between them creates a very different acoustic result. Identifying this mechanism required high-speed footage, since the motion happens too quickly for the human eye to parse in real time.
A rare percussion club in the animal kingdom
The scissor-tailed nightjar now joins a small and unusual group: birds that use their bodies, rather than their voices, to produce sound. It is a shorter list than most people might expect.
Male Siberian grouse (Falcipennis falcipennis) strike their uniquely shaped wing feathers together, while male riflebirds scrape their bill across their wings in a motion resembling wood dragged across a rasp. The nightjar’s specific technique — snapping the wrist bones together — places it in an even more exclusive category. The only other birds known to use this same mechanism are certain manakins, colorful birds found across tropical America. That two distantly related groups independently arrived at the same solution suggests non-vocal sound production offers real advantages, enough that evolution found its way there more than once.
What the snaps are saying — and what remains unknown
Researchers have mapped out when males snap, even if the full meaning remains unclear. The sounds appear during mate attraction, during mating itself, and when chasing away intruders — a range of contexts suggesting the snaps carry real communicative weight. What specific information they convey to other nightjars, though, is still an open question.
Areta noted something almost affectionate in the birds’ relationship to the sound: “It seems that nightjars are really fond of these sounds.”
Whether different snap patterns carry different meanings, how females respond, what they are actually listening for — none of that is settled yet. Those questions point toward the next phase of study. As high-speed camera technology becomes more accessible for fieldwork, the answers may not be far off, and this small, long-tailed bird may have more to say than anyone expected.