The acoustic structure and possible mechanical origin of the male Corncrake call

Robert Malcolm Arnold 

The male Corncrake Crex crex produces a distinctive repetitive call whose acoustic structure suggests a mechanically constrained sound-production system rather than a conventional tonal vocalisation. Here I describe observations obtained from approximately 800 field recordings made on Skye between 2020 and 2026 and develop a testable hypothesis for the origin of the long-duration and repetitive acoustic structure of the call. A provisional mechanism is proposed in which rapid closure and opening of alternate syrinx lumens, by a self-oscillating part of the syrinx, generate transient vibration of the tympaniform membranes, with the interclavicular air sac and suprasyringeal vocal tract contributing to resonance and radiation. The mechanism is compared conceptually with the echlocating click-production mechanism described for the Australian Grey Swiftlet. The present study is hypothesis-generating and does not include direct anatomical observations required to establish the proposed mechanism.