Effects of multiple-speaker playbacks on aggressive calling behavior in the treefrog Dendropsophus ebraccatus

Abstract

In addition to producing signals, males of chorusing species also act as receivers by adjusting properties of their vocalizations in response to those of other nearby individuals. Although it is likely that males are responsive to more than one other individual, most playback studies investigating male response have involved dyads in which vocal responses are measured to stimuli presented from a single speaker. In this study, I explored changes in both the propensity to give aggressive calls and the temporal properties of those calls in response to the playback of multiple aggressive call stimuli in the treefrog Dendropsophus ebraccatus. I found that males were sensitive to both the number of simulated aggressive callers and their specific call characteristics. Males generally gave a highly aggressive response to the first stimulus presented, but their response to the modification of this stimulus by the addition or subtraction of a simulated competitor depended on the degree of aggressiveness of the stimuli. Males tended to decrease their aggressive responses when either a more aggressive call was silenced or a less aggressive call was added and to increase their aggressive responses in the opposite situation. Aggressive calling in this species is clearly affected by complex changes in the social environment and I suggest that future studies explore these issues in other species to improve the understanding of communication interactions.