We investigated individual, nightly, and seasonal variation in calling behavior of a population of gray tree frogs (Hyla versicolor) from Connecticut, USA. Repeated recordings of individual males on seven nights revealed significant differences among males in calling rate on all but one night and differences in number of pulses per call and number of pulses produced per hour (pulse effort) on four nights. Most males reduced calling activity late at night (after 2230 h), but some maintained a relatively steady rate of call production before dropping out of the chorus. Data collected for 26 individuals recorded on three or more nights throughout the breeding season revealed significant differences among males in calling rate, number of pulses per call, and pulse effort, but repeatabilities for all three variables were low (0.17, 0.35, and 0.12, respectively). The highest repeatability was for number of pulses per call, a variable strongly influenced by proximity to calling neighbors, probably because males often interacted with neighbors at similar distances on several successive nights. Males tended to reduce the number of pulses per call as the season progressed and the distance between neighbors decreased, but they showed no clear seasonal change in calling rate or pulse effort. There was a substantial seasonal decline in the number of hours of chorus activity, resulting in a median decrease of 43% in nightly energy expenditure by calling males.

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