Vocal learning in songbirds is thought to have evolved through sexual selection, with female preference driving males to develop large and varied song repertoires^1,2,3. However, many songbird species learn only a single song in their lifetime⁴. How sexual selection drives the evolution of single-song repertoires is not known. Here, by applying dimensionality-reduction techniques to the singing behaviour of zebra finches (Taeniopygia guttata), we show that syllable spread in low-dimensional feature space explains how single songs function as honest indicators of fitness. We find that this Gestalt measure of behaviour captures the spectrotemporal distinctiveness of song syllables in zebra finches; that females strongly prefer songs that occupy more latent space; and that matching path lengths in low-dimensional space is difficult for young males. Our findings clarify how simple vocal repertoires may have evolved in songbirds and indicate divergent strategies for how sexual selection can shape vocal learning.

鸣禽的声音学习被认为是通过性选择进化而来的，雌性的偏好驱使雄性发展出大量多样的歌曲曲目^1,2,3。然而，许多鸣禽在其一生中只学会一首歌曲⁴。性选择如何推动单曲曲目的进化尚不清楚。在这里，通过将降维技术应用于斑胸草雀（Taeniopygia guttata）的歌唱行为，我们证明了低维特征空间中的音节传播解释了单首歌曲如何充当诚实的健康指标。我们发现，这种格式塔行为测量捕捉了斑胸草雀歌曲音节的频谱时间独特性；女性强烈喜欢占据更多潜在空间的歌曲；对于年轻男性来说，在低维空间中匹配路径长度是很困难的。我们的研究结果阐明了鸣禽中简单的声音曲目是如何进化的，并表明性选择如何塑造声音学习的不同策略。