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 song to assess
the distance of its singer requires a receiver to discriminate between
different degrees of degradation by taking into account the acoustical
properties of the habitat. Ranging accurately when acoustical properties
change seasonally then requires a receiver to reassess previous
associations of degradation with distance.
Here I tested the possibility that Carolina wrens (Thryothorus
ludovicianus) discriminate between different levels of song
degradation and change their association of degradation with distance when
the acoustical properties of their territories change.
In response to playback of a single song, either undegraded or degraded
(at two different levels), most subjects flew to the far side of the
loudspeaker only in response to degraded songs. In addition, behavioral
responses beyond the loudspeaker were consistently 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 association of degradation with distance
as habitat conditions changed.
Such adjustment of associating a given level of degradation with distance
is an important requirement for accurate ranging, in particular under
changing acoustical conditions of the environment. In addition, rapid
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.