Determination of the wingsnap sonation mechanism of the golden-collared manakin (Manacus vitellinus)

Male golden-collared manakins (Manacus vitellinus), small suboscine passeriform birds of Panamanian forests, communicate acoustically using a variety of non-vocal sonations. The most prominent sonations are single or multiple intense 'wingsnaps' with a dominant acoustic frequency around 5 kHz. Several hypotheses have been proposed addressing the source of the sound, ranging from purely aerodynamic origins (due to a rapid jet of air formed by the wings or by a 'whiplike' motion) to purely structural origins (such as physical contact of the wings), but without definitive assessment. Using anatomical analysis as well as high-speed video and synchronized audio recordings, we show that compared with related species, M. vitellinus radii are morphologically unique and confirm that they collide over the back of the bird at the moment (+/- 1 ms) the wingsnap is produced. Using aeroacoustic theory, we quantitatively estimate the acoustic signatures from several sonation mechanisms. We conclude that only the physical contact hypothesis, wherein the wing collisions create the sound, is consistent with the measured sonation.