SONG TRANSMISSION AND AUDITORY-PERCEPTION OF DISTANCE IN WOOD WARBLERS (PARULINAE)

The influence of breeding habitat on the evolution of song structure w as 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 investi gated. Song transmission characteristics of paruline breeding habitats were compared in southeastern Ontario, Canada; songs native to the ha bitat in which they were broadcast did not degrade less than foreign s ongs. The response of territorial paruline males to playback of 'near' (undegraded) and 'far' (degraded) conspecific songs broadcast from th e same position within the territory at the same amplitude were then c ompared. 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 experim ents are discussed with respect to the ranging hypothesis, which propo ses that selection should favour males that structure songs to minimiz e their degradation, so that songs function to disrupt or intimidate r ivals by providing unreliable distance cues. (C) 1997 The Association for the Study of Animal Behaviour.