Abstract:

This work presents a comparison across selected species of several aspects of the mechanism of sound radiation in frogs. Measurements of the magnitude of the transfer function of the radiating structures show that the structures radiating the bulk of the energy present in the call vary depending on the species. Bullfrogs (Rana catesbeiana) radiate most of the energy (89% sound level) in their calls through their eardrums. Additionally, the transfer function of the eardrums displays peaks coincident with those observed in the mating and release call of this species. The vocal sac and gular area contribute energy only in the lower band (150--400 Hz). The ears are responsible for radiating additional frequency bands to the ones radiated through the vocal sacs. In Rana pipiens, the ears also broadcast a significant portion of the energy present in the call (63% sound level), but the frequencies of the aural emissions are a subset of those frequencies radiated through the vocal sacs. Finally, the barking treefrog (Hyla gratiosa) appears to use two different structures to radiate his call. The low-frequency band is preferentially radiated through the lungs while the high-frequency components are radiated through the vocal sac.