Using bond graphs to model vocal production in túngara frogs

Abstract

Male anurans (frogs and toads) produce species-specific advertisement calls. Conceptual models illustrate how anurans produce calls, but quantitative models of vocal production are rare. Consequently, how frogs produce complex or nonlinear signals, and how differences in morphology result in call differences among species, is in many cases unclear. Bond graphs are representations of dynamic physical systems that allow one to model both the hydraulic elements and mechanical oscillators of air-driven vocal production systems. They can be used to model either single components or interactions among components within vocal systems. This paper uses túngara frogs to show how bond graphs can be used to model vocal production. Túngara frogs produce complex calls that contain a species-specific “whine” and a facultative “chuck”. Their calls are frequency- and amplitude-modulated, and exhibit nonlinearities. A bond graph model of the túngara vocal folds produces sustained oscillations at a frequency typical of this frog. The complexity of the túngara frog call is explained by modulating the behavior of integrated components within its vocal production system. The bond graph modeling approach can be used to understand how the biomechanics of vocal production underlies the diversity of animal signals.