Acoustic interactions among male gray treefrogs, Hyla versicolor, in a chorus setting
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We assembled groups of up to eight male gray treefrogs, Hyla versicolor, in an artificial pond and examined vocal behavior under conditions of different chorus size. Males avoided call overlap when calling in groups of two, but not in larger choruses. The pattern of interference failed to reveal selective attention based on inter-male separation, and males in close spatial proximity tended to overlap calls more than more widely separated individuals did. Males were sensitive to the removal of males from or the addition of males to an aggregation, often responding to a change of just one individual with shifts in call duration and rate. Nevertheless, males tended to maintain their relative position in a hierarchy based on call duration following changes in chorus size. We hypothesize that adjustments in gross temporal properties are a response to the increased probability of call interference in larger choruses. Finally, we calculated repeatabilities of call duration, calling rate, and pulse effort within nights using sliding-analysis windows of 30 s to 29.5 min. The change in repeatabilities with window duration suggests that a female could best distinguish among males by assessing their performance for between 4 and 14 min, depending on the measure of calling behavior. However, because the magnitude of change was relatively small, our data do not lend strong support to the hypothesis that there is an optimum time period over which females should assess the calling of males in order to maximize their ability to discriminate among males.
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