RANGING OF SONGS WITH THE SONG TYPE ON USE OF DIFFERENT CUES IN CAROLINA WRENS - EFFECTS OF FAMILIARITY

Male territorial song birds are usually spaced far apart and most ofte n hear conspecific song after it has been degraded by propagation thro ugh the environment. Their ability to use the degradation of songs to assess the distance of a singing rival without approaching (called ran ging) presumably increases the efficiency of defending a territory. In order to assess degradation in a song the receiver needs to compare t he characteristics of the received song to its characteristics at the source or at different distances. Earlier experiments on ranging in sp ecies with song repertoires have suggested that prior familiarity with the particular song type is necessary for ranging. Here I show that m ale Carolina wrens (Thryothorus ludovicianus) can use either temporal or spectral characteristics for ranging song types which they were unl ikely to have heard previously. Playbacks consisting of only one song prevented subjects' close-range experience with the loudspeaker, and f lights beyond the loudspeaker provided direct evidence for over-assess ment of distance when songs were degraded. Because ranging of songs wa s not affected by the degree of familiarity with the song type, this e xperiment provides no evidence that song repertoires hinder ranging in Carolina wrens, as suggested by Morton's ranging hypothesis. Instead, at least approximate ranging of songs is evidently possible by assess ment of degradation in general features of a species' songs.