Ranging of songs with the song type on use of different cues in Carolina wrens: effects of familiarity
Behavioral Ecology and Sociobiology
Male territorial song birds are usually spaced far apart and most often hear conspeci®c song after it has been degraded by propagation through the environment. Their ability to use the degradation of songs to assess the distance of a singing rival without approaching (called ranging) presumably increases the eciency of defending a territory. In order to assess degradation in a song the receiver needs to compare the characteristics of the received song to its characteristics at the source or at
... ierent distances. Earlier experiments on ranging in species with song repertoires have suggested that prior familiarity with the particular song type is necessary for ranging. Here I show that male Carolina wrens (Thryothorus ludovicianus) can use either temporal or spectral characteristics for ranging song types which they were unlikely to have heard previously. Playbacks consisting of only one song prevented subjects' closerange experience with the loudspeaker, and¯ights beyond the loudspeaker provided direct evidence for over-assessment of distance when songs were degraded. Because ranging of songs was not aected by the degree of familiarity with the song type, this experiment 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 assessment of degradation in general features of a species' songs.