Data from: The effect of social environment on bird song: listener-specific expression of a sexual signal

Animal signals should consistently differ among individuals to convey
distinguishable information about the signalers. However, behavioral
display signals, such as bird song are also loaded with considerable
within-individual variance with mostly unknown function. We hypothesized
that the immediate social environment may play a role in mediating such
variance component, and investigated in the collared flycatcher (Ficedula
albicollis) if the identity and quality of listeners could affect song
production in signalers. After presenting territorial males with either a
female or male social stimulus, we found in the subsequent song recordings
that the among-stimulus effects corresponded to non-zero variance
components in several acoustic traits indicating that singing males are
able to plastically adjust their songs according to stimulus identity.
Male and female stimuli elicited different responses as the identity of
the female stimuli affected song complexity only, while the identity of
male stimuli altered also song length, maximum frequency and song rate.
The stimulus-specific effect on song in some cases decreased with time,
being particularly detectable right after the removal of the stimulus and
ceasing later, but this pattern varied across the sex of the stimulus and
the song traits. We were able to identify factors that can explain the
among-stimulus effects (e.g. size and quality of the stimuli) with roles
that also varied among song traits. Our results confirm that the variable
social environment can raise considerable variation in song performance,
highlighting that within-individual plasticity of bird song can play
important roles in sexual signaling.