Male scissor-tailed nightjars (Hydropsalis torquata) produce high-intensity, percussive snapping sounds by colliding their wing bones together during flight, according to research published in the Journal of Avian Biology. This mechanical sound production serves as a specialized mating signal, allowing the nocturnal birds to communicate despite their typically silent flight patterns.
How Scissor-Tailed Nightjars Create Sound
Researchers Juan Ignacio Areta of the Instituto de Bio y Geosciencias del Noroeste Argentino and Christopher Clark of the University of California, Riverside, confirmed that these birds generate sound through a physical impact rather than vocalization. Using high-speed infrared cameras to observe the birds in the Andean foothills near Salta, Argentina, the team documented the nightjars swinging their wings behind their backs during flight.
The audible "crack" occurs when the birds’ wrist bones collide. Unlike many other bird species that produce sound by vibrating feathers or scraping bills against wings, the scissor-tailed nightjar relies on the forceful impact of skeletal structures. The vibration resulting from this bone-on-bone contact creates the sharp, rhythmic noises observed by the researchers in late 2022.
Why Nightjars Use Percussive Communication
While nocturnal animals are often associated with silent movement—such as the specialized feather structures that allow owls to hunt without detection—the scissor-tailed nightjar deviates from this norm. According to the study, these sounds are primarily linked to reproductive behaviors.
Males perform these wing-snaps in several specific social contexts:
- Courtship: Attracting potential mates during nighttime hours.
- Mating: Ongoing signaling during reproductive acts.
- Territorial Defense: Chasing away intruders who enter the male’s established space.
Comparison to Other Percussive Bird Species
The scissor-tailed nightjar joins a distinct group of avian species that utilize non-vocal, mechanical sounds for communication. While vocalizations remain the standard for most birds, specific lineages have evolved physical adaptations for sound production:
| Species | Mechanism |
|---|---|
| Siberian Grouse | Strikes uniquely shaped wing feathers together. |
| Riflebirds | Scrapes the bill across the wing surface. |
| Manakins | Snaps wrist bones together, similar to the nightjar. |
According to Dr. Areta, the scissor-tailed nightjar is one of the few known species to utilize a wrist-snapping mechanism similar to that of the manakin family. This evolutionary development allows the birds to broadcast their presence in low-light environments where visual signaling would be ineffective.
Research Implications
This study clarifies a long-standing question regarding how nocturnal birds maintain acoustic signals without relying on vocal cords. By documenting the physical mechanics of the wing-snap, researchers have established that these birds prioritize auditory signals to navigate complex mating rituals in the dark. Future studies may focus on whether female nightjars exhibit specific auditory preferences for the frequency or intensity of these mechanical snaps, further explaining the evolutionary pressure behind this unique behavior.