The role of the environment on the acoustic radiation patterns of mating calls of the túngara frog

The present work is a follow-up to previously reported [J. Acoust. Soc. Am. 122, 2981(A) (2007)] laboratory measurements of both the horizontal and vertical frequency-dependent directivity of the mating calls of túngara frogs, Physalaemus pustulosus. Band-limited directivities are significantly greater than broadband directivities, with a maximum directivity of 20 dB in the vertical plane for harmonics near 6 kHz. This result is unexpected given that female frogs, the intended receivers of this call, are on the horizontal plane rather than on the vertical plane where unintended receivers (predators and parasites) reside. New numerical finite element modeling of the radiation, including the effects of the environment, will be reported. Túngara frogs only call while partially submerged in water. Modeling results indicate that the reflecting boundary provided by a finite-sized air-water interface dominates the radiation, and results in the observed directivity. There is comparatively little directivity dependence on the nature of the surrounding terrain, be it acoustically hard or soft, smooth or rough. These modeling results indicate that the radiation patterns found in laboratory measurements, although unexpected, are likely to be found in nature too.