USE OF SONG AMPLITUDE FOR RANGING IN CAROLINA WRENS, THRYOTHORUS-LUDOVICIANUS

Songbirds are well known to use the degradation of conspecific song to assess the distance of the singer (called ranging). Because a song's degradation accumulates progressively with propagation distance and th us is not under direct control of the singer, it potentially provides more reliable distance information than the amplitude of songs. Howeve r, song amplitude decreases progressively with distance and thus also provides information about the singer's distance, provided that interf erence from wind is low and that the sender does not alter broadcast v olume. This study investigated whether or not Carolina wrens, Thryotho rus Indomicanus, can use changes in amplitude of conspecific song as a relative cue for ranging. Twelve male subjects each received one play back consisting of two successive songs differing by 6 dB in amplitude . Half the subjects received playbacks with the louder song first and the other half received playbacks with the louder song second. Receive rs that would use song amplitude for ranging would perceive the simula ted rival either as approaching or retreating depending on whether the louder song was played first or second. Subjects responded as ii the rival was farther away in the simulated retreat than in the simulated approach, indicating that Carolina wrens can use differences in amplit ude of successive songs for ranging. Apparently, the risk of inaccurat e ranging by song amplitude is outweighed hi; the advantage of using m ultiple cues, including information from song amplitude, to assess a r ival's distance.