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.

中文翻译：

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社会环境对鸟鸣的影响：性信号的特定听众表达

动物信号在个体之间应该始终不同，以传达有关信号者的可区分信息。然而，行为显示信号，如鸟鸣，也充满了相当大的个体差异，其中大部分是未知的功能。我们假设直接的社会环境可能在调解这种方差分量中发挥作用，并在有领的捕蝇器 ( Ficedula albicollis)中进行了调查) 如果听众的身份和质量会影响信号员的歌曲制作。在向领地男性提供女性或男性社会刺激后，我们在随后的歌曲录音中发现，刺激间效应对应于几个声学特征中的非零方差分量，表明唱歌的男性能够根据刺激身份。男性和女性刺激引起不同的反应，因为女性刺激的身份仅影响歌曲的复杂性，而男性刺激的身份也会改变歌曲长度、最大频率和歌曲率。在某些情况下，特定刺激对歌曲的影响会随着时间的推移而减弱，在移除刺激并稍后停止后特别明显，但这种模式因刺激的性别和歌曲特征而异。我们能够确定可以解释刺激间效应（例如，刺激的大小和质量）的因素，其作用在歌曲特征之间也有所不同。我们的结果证实，多变的社会环境可以引起歌曲表现的相当大的变化，强调鸟鸣的个体可塑性可以在性信号中发挥重要作用。