Mechanics of sound production in toads of the genus Bufo: Passive elements

Abstract The vibration mechanics of the vocal tracts of over 40 species of toads (genus Bufo) were studied, using an apparatus to artificially activate the larynges of freshly killed animals. The effects of laryngeal ablations on the mating and release calls were studied. They confirmed the results obtained by artificial activation. The mating and release call dominant frequencies are determined primarily by the fundamental frequencies of vibration of the paired vocal cords. Vocal cord resonant frequencies are in turn largely determined by the activation air pressure and the masses of cartilagenous deposits in their lateral portions. In most species, fleshy folds within the larynx at the anterior extremities of the arytenoid cartilages cause these cartilages to vibrate during sound production, amplitude modulating the vocal cord output. In most species, the contraction pattern of the vocal musculature is reflected as a periodic pulsation. Frequency modulations of the mating call dominant (or carrier) frequency are described, partially explained, and deemphasized in importance with respect to toad acoustical communication. The findings of this investigation are made relevant to the overall problem of the structure and evolution of toad acoustical communication by use of an analogy with standard AM radio broadcast.