Goto Hana, Soma Masayo, Mizuno Ayumi, Brumm Henrik
Graduate School of Life Science, Hokkaido University, Sapporo, Hokkaido, Japan.
Faculty of Science, Hokkaido University, Sapporo, Hokkaido, Japan.
PeerJ. 2025 Jul 10;13:e19705. doi: 10.7717/peerj.19705. eCollection 2025.
Given the two main functions of birdsong, mate attraction and territory defence, song amplitude is crucial for communication because it determines the communication range and it can also carry information. To understand the evolution of signals, it is helpful to consider the constraints on signal production, as physical constraints set the limits for signal plasticity and how signals can respond to selection. Previous work on the constraints of song amplitude was restricted to species that use loud vocalisations for long-distance communication. However, the low song amplitudes of some non-territorial species may hint at unknown limitations considering that females may prefer loud song. The star finch () is one such species. In this study, we recorded the songs of male star finches in the laboratory and investigated the relationship between vocal amplitude and other acoustic parameters of their song syllables. We found that vocal amplitude was linked to the phonetic structure of the syllables. More complex sounds (measured as higher syllable bandwidth and higher Wiener entropy) were produced at lower amplitudes than less complex sounds. To the best of our knowledge, this is the first report of a trade-off between song complexity and vocal amplitude. More complex song syllables possibly require a more intricate control of the syrinx and vocal tract, which might only be possible at lower amplitudes. We speculate that if female star finches prefer complex songs, this would cause males to sing quietly, as they cannot produce complex syllables with high amplitudes. We also provided a phonetogram (vocal range profile) for the star finch, indicating a positive correlation between amplitude and peak frequency. This finding corroborates earlier studies on species that use loud vocalisations for long-range communication, which, like the star finches in our study, were also unable to produce low frequencies at high amplitudes. This suggests that the frequency-amplitude correlation is a more general phenomenon in bird vocalisations, independent of the overall source amplitude of a species. While the evolution of birdsong is often viewed as constrained by neural costs and body size, or selective pressures from predators and social aggression, our results emphasise the importance of understanding phonetic features as well. At the same time, our study fills an important gap on non-territorial species that produce soft songs. The absence of the ecological demands for long-distance signalling has probably led birds to use soft yet complex songs that function within the pair bond, as we report here for star finches.
鉴于鸟鸣的两个主要功能，即吸引配偶和保卫领地，鸣声幅度对于交流至关重要，因为它决定了交流范围，并且还能传递信息。为了理解信号的进化，考虑信号产生的限制因素是有帮助的，因为物理限制设定了信号可塑性的限度以及信号如何响应选择。先前关于鸣声幅度限制的研究仅限于那些使用大声鸣叫进行远距离交流的物种。然而，一些非领地性物种的低鸣声幅度可能暗示着未知的限制，因为雌性可能更喜欢大声的鸣叫。星雀（学名：Neochmia ruficauda）就是这样一种物种。在本研究中，我们在实验室记录了雄性星雀的鸣声，并研究了鸣声幅度与它们歌声音节的其他声学参数之间的关系。我们发现鸣声幅度与音节的语音结构有关。与不太复杂的声音相比，更复杂的声音（以更高的音节带宽和更高的维纳熵来衡量）是在较低幅度下产生的。据我们所知，这是关于歌声复杂性和鸣声幅度之间权衡的首次报道。更复杂的歌声音节可能需要对鸣管和声道进行更精细的控制，而这可能仅在较低幅度下才有可能。我们推测，如果雌性星雀更喜欢复杂的歌声，这将导致雄性轻声歌唱，因为它们无法在高幅度下发出复杂的音节。我们还为星雀提供了一个声谱图（鸣声范围剖面图），表明幅度与峰值频率之间存在正相关。这一发现证实了先前对那些使用大声鸣叫进行远距离交流的物种的研究，这些物种与我们研究中的星雀一样，也无法在高幅度下发出低频声音。这表明频率 - 幅度相关性在鸟类鸣叫中是一种更普遍的现象，与一个物种的整体声源幅度无关。虽然鸟鸣的进化通常被认为受到神经成本和体型的限制，或者来自捕食者和社会攻击的选择压力的限制，但我们的结果强调了理解语音特征的重要性。同时，我们的研究填补了关于发出轻柔歌声的非领地性物种的一个重要空白。正如我们在此报道的星雀一样，缺乏对远距离信号传递的生态需求可能导致鸟类使用柔和但复杂的歌声，这些歌声在配偶关系中发挥作用。
