Phonotaxis in Hyla versicolor (Anura, Hylidae): the effect of absolute call amplitude.

The influence of call amplitude on phonotaxis in female Hyla versicolor was studied using a no-choice paradigm. One set of experiments estimated effects of stimulus amplitude on phonotaxis toward a synthetic model of a conspecific call. The response strength increased with amplitude from the behavioral threshold (37-43 dB SPL) up to 79 dB SPL and then decreased at higher amplitudes. Females approached the loudspeaker with short walking bouts (approximately 1 s duration) occurring immediately after call presentations. Increase in response strength was attributed to an increasing proportion of calls that elicited such walking bouts, whereas the decrease at high amplitudes resulted from decreasing distance covered per bout. The quality of orientation remained constant for all above-threshold amplitudes. A second set of experiments tested the selectivity for interval duration and pulse duration at amplitudes of 55, 70, and 85 dB SPL. Selectivity for both parameters was similar at 70 and 85 dB SPL, but tended to increase at 55 dB SPL. The results suggest that selective phonotaxis in H. versicolor is not adapted for long-distance communication. This finding differs from those of comparable studies of acoustic insects.