Degradation of wren <i>Troglodytes troglodytes</i> song: Implications for information transfer and ranging

Abstract

The effects of bird song imply a transfer of information between conspecifics. This communication channel is constrained by habitat-induced degradation. Many studies suggest that birds can utilize features of degraded song to assess relative distance to the signaller (ranging). The degradation of transmitted song in the wren Troglodytes troglodytes is quantified to assess the opportunities offered in received song for both information transfer and ranging. This quantification incorporates three measurable aspects of degradation: signal-to-noise ratio; excess attenuation; blur ratio. Each aspect varies more-or-less predictably with transmission distance, i.e., a criterion for ranging. Significant effects of speaker and microphone elevation indicate a potential for birds to optimize both the opportunity for information transfer and ranging by considering perch location. Song elements are the smallest units of a song being defined as a continuous trace on a sonagram. Main and second-order effects of element type indicate element-specific patterns of degradation which could be a crucial factor in communication in this species. The element variation within a full song offers the potential for effective information transfer over a range of relevant distances and a variety of transmission pathways. It similarly offers highly flexible ranging opportunities.