Call timing is determined by response call type, but not by stimulus properties, in the treefrog Dendropsophus ebraccatus

Abstract

A common form of signal competition in acoustically chorusing animals involves the precise timing of calls relative to those of other nearby individuals. In this study, I present a detailed description of nonrandom timing of both advertisement and aggressive calls in males of the Neotropical treefrog Dendropsophus ebraccatus. I used playback tests to measure call delays for both advertisement and aggressive calls given in response to synthetic advertisement and aggressive call stimuli presented with either a fixed or random timing arrangement. Call delays for a given response call type were nonrandomly distributed and did not differ depending on the fixed or random periodicity of stimulus presentation or on the stimulus call type. In general, advertisement call responses overlapped the playback stimuli, while aggressive calls were given with a much longer delay and did not overlap the playback stimuli. A second test involved the presentation of low pulse number advertisement and aggressive call stimuli to determine if males were capable of nonrandom timing to truncated stimuli. These playbacks also assessed whether they responded more aggressively to truncated aggressive call stimuli. Males usually showed synchrony in response to truncated calls of both types, more commonly in response to truncated advertisement calls. There were no differences in aggressive responses to truncated advertisement or aggressive calls. Call delays appear to be a property solely of the type of call that the male produces, regardless of the kind of stimulus. Thus, there may be a conflict between the ability to discriminate between signals and the ability to rapidly respond to these signals with an appropriate call delay.