Song transmission and auditory perception of distance in wood warblers (Parulinae)

The influence of breeding habitat on the evolution of song structure was examined in four wood warbler species of the sub-family Parulinae. The effects of song degradation on the ability of territorial paruline males to estimate distance by means of acoustic cues was also investigated. Song transmission characteristics of paruline breeding habitats were compared in southeastern Ontario, Canada; songs native to the habitat in which they were broadcast did not degrade less than foreign songs. The response of territorial paruline males to playback of 'near' (undegraded) and 'far' (degraded) conspecific songs broadcast from the same position within the territory at the same amplitude were then compared. Males responded to near songs as they would to a conspecific territorial intruder and with less intensity to far songs, suggesting that males may use cues from song degradation to estimate distance to vocal conspecifics. Our results from transmission and playback experiments are discussed with respect to the ranging hypothesis, which proposes that selection should favour males that structure songs to minimize their degradation, so that songs function to disrupt or intimidate rivals by providing unreliable distance cues.