How Nightjars produce loud wing-snaps during courtship

CLARK CJ; ARETA JI

Seattle

Congreso; ISCB2024; 2024

Society for Integrative and Comparative Biology

Many species of nightjar reportedly produce ‘clapping’ sounds with theirwings during courtship. To record these displays, we illuminated N = 6 maleScissor-tailed Nightjars (Hydropsalis torquata) with infrared light on a roadnear Salta, Argentina, in spring and early summer (Sept-Dec 2022) on pre-dawn nights immediately following a full moon. Amongst the moonlight, thenightjars produced 4 different types of nonvocal sound, the most commonof which were short, sharp, loud, atonal ‘tk’ sounds. These sounds wereproduced in multiple contexts: during a jump display, in a flight display, andimmediately after copulation. High-speed video revealed these ‘tk’ soundswere produced when a bird rapidly elevated and pronated his wings to slamopposing wrists together. The videos falsify the hypothesis that sound isproduced by clapping, i.e. a pulse of air accelerating to escape a constrictedspace (as in human hand-clapping), as there was no contact by the surface ofopposing wing-feathers. Instead, we conclude the physical acoustic mecha-nism is likely snapping, i.e. impulsive collisions between stiff elements (wingbones) which then vibrate, similar to wing-snapping of Manacus manakins. Wefinish by speculating about whether other birds produce snapping or clapping.There is acoustic evidence that hints many species of nightjar in the genusCaprimulgus do produce wing clapping, as do certain owls and possibly ahummingbird.