Signal jamming mediates sexual conflict in a duetting bird.

Signal evolution in social animals has produced a wide variety of communal displays, many of them remarkable feats of complex coordination. The two main explanations for this temporal precision are: (1) it evolves as a cooperative signal of coalition quality or (2) it minimizes signal jamming (i.e., interference of one signal by another). However, support for the first hypothesis is inconclusive, and the role of jamming in communal signaling strategies remains unknown. Here, we use playback experiments to examine how social context influences the structure of duets in a pair-living antbird (Hypocnemis peruviana). The results show that, although resident pairs produced coordinated duets when responding to rival pairs, conflicts of interest caused duet coordination to break down. Specifically, females responded to unpaired sexual rivals by jamming the signals of their own mates, who in turn compensated by adjusting their signals to avoid interference. In demonstrating this interaction, we provide the first evidence that signal jamming occurs between mates and that strategies for reducing jamming can result in increased signal complexity. These findings highlight the importance of jamming avoidance in determining the structure of duets and suggest that conflict between signalers, rather than cooperation alone, may drive the evolution of sophisticated communal displays in social animals.