RANGING BY SONG IN CAROLINA WRENS THRYOTHORUS LUDOVICIANUS - EFFECTS OF ENVIRONMENTAL ACOUSTICS AND STRENGTH OF SONG DEGRADATION

Territorial male song birds most frequently hear conspecific song that has been degraded (distorted) by transmission through the environment . Their ability to use this accumulated degradation in conspecific son g to assess the distance of its singer requires a receiver to discrimi nate between different degrees of degradation by taking into account t he acoustical properties of the habitat. Ranging accurately when acous tical properties change seasonally then requires a receiver to reasses s previous associations of degradation with distance. Here I tested th e possibility that Carolina wrens (Thryothorus ludovicianus) discrimin ate between different levels of song degradation and change their asso ciation of degradation with distance when the acoustical properties of their territories change. In response to playback of a single song, e ither undegraded or degraded (at two different levels), most subjects flew to the far side of the loudspeaker only in response to degraded s ongs. In addition, behavioral responses beyond the loudspeaker were co nsistently stronger to playback of degraded songs than to playback of undegraded songs. Responses indicate that wrens discriminated between different levels of degradation and suggest that they adjusted their a ssociation of degradation with distance as habitat conditions changed. Such adjustment of associating a given level of degradation with dist ance is an important requirement for accurate ranging, in particular u nder changing acoustical conditions of the environment. In addition, r apid ranging on the basis of only one song might facilitate processing of additional information such as a singers identity and motivation. Resulting selective attention to the closest rival might increase the reliability or speed of decoding such additional information.