Behavioral vocal response thresholds to mating calls in the bullfrog, R a n a c a t e s b e i a n a

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Abstract
Male bullfrogs will vocalize in response to playbacks of the mating (advertisement) calls of conspecifics. This behavior was studied in response to playbacks of bullfrog mating cells presented at 6 different sound intensity levels. The lowest sound intensity level tested [50 dB SPL (sound pressure level)] was insufficient to evoke calling from any of the animals. Calling was evoked by playback levels of 60 dB SPL and higher. Behavioral evoked calling thresholds may lie between 50-60 dB SPL for these animals. Playback intensity levels of 80 dB SPL were more effective in evoking responses than were intensity levels up to 20 dB higher or lower. This was true both in terms of the total number of evoked responses and the trial number at which responding ceased. Moreover, significantly less habituation of evoked calling occurred at levels of 80 dB SPL than at higher or lower levels. A SPL of 80 dB apparently represented a behaviorally preferred intensity level for evoked calling in the bullfrog. Field recordings of bullfrog choruses showed that the intensity produced by an individual calling male reached 80 dB SPL at a distance of 1 m. This intensity level was identical to that producing maximal evoked calling in the laboratory.