Socially mediated plasticity in call timing in the gray tree frog, Hyla versicolor

Call timing is an important component of the behavioral repertoire of many chorusing species that compete acoustically for mates. The costs and benefits of particular call-timing patterns may vary with factors in the social environment, yet few studies have examined the possibility of socially mediated plasticity in call timing. We studied the effects of competition on advertisement-call timing in the gray tree frog, Hyla versicolor, by manipulating intermale distances in staged interactions. We measured phase angles and the proportion of calls that overlapped as interacting pairs of males were moved closer to one another, simulating an increase in acoustic competition. We observed a shift in phase angle resulting in substantially higher levels of overlap as males were moved so that they were calling at extremely close range. At close range, males often engage in intense agonistic contests over the calling space and we found that call timing may play a role in these interactions. Although there were not major differences in the call-timing behavior of winners and losers of contests, we suggest that call overlap may be a general signal of aggressive motivation. Changes in call timing with changes in intermale distance may, therefore, be related to changes in the intended audience as competition escalates.