Songbird cheaters pay a retaliation cost: evidence for auditory conventional signals

Conventional signals impose costs on senders through receiver retaliation r ather than through investment in signal production. While several visual co nventional signals have been described (mainly 'badges of status'), acousti c examples are rare; however, several aspects of repertoire use in songbird s are potential candidates. We performed interactive playback experiments t o determine whether song-type matches (responding to a song with the same s ong type), repertoire matches (responding to a song with a different song t ype, but one in the repertoires of both singers) and unshared song types se rve as conventional signals during male-male territorial interactions in ba nded wrens, Thryothorus pleurostictus. Our results demonstrate that these t hree signals incite varying levels of receiver aggression: song-type matche s induce faster approach than do repertoire matches, and repertoire matches induce faster approach than do unshared song types. Production costs do no t differ, while the receiver response does. Because territorial banded wren s approach opponents who signal aggressively, such opponents risk attack. T his system will punish and prevent cheaters, as weak males signalling aggre ssion will be subject to escalation by stronger or more-motivated opponents .