Use of Song Amplitude for Ranging in Carolina Wrens, Thryothorus ludovicianus

Abstract

AbstractSongbirds 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 thus is not under direct control of the singer, it potentially provides more reliable distance information than the amplitude of songs. However, song amplitude decreases progressively with distance and thus also provides information about the singer's distance, provided that interference from wind is low and that the sender does not alter broadcast volume. This study investigated whether or not Carolina wrens, Thryothorus ludovicianus, can use changes in amplitude of conspecific song as a relative cue for ranging. Twelve male subjects each received one playback 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. Receivers that would use song amplitude for ranging would perceive the simulated rival either as approaching or retreating, depending on whether the louder song was played first or second. Subjects responded as if the rival was farther away in the simulated retreat than in the simulated approach, indicating that Carolina wrens can use differences in amplitude of successive songs for ranging. Apparently, the risk of inaccurate ranging by song amplitude is outweighed by the advantage of using multiple cues, including information from song amplitude, to assess a rival's distance.