Vocal learning in songbirds is thought to have evolved through sexualselection, with female preference driving males to develop large and varied songrepertoires1–3. However, many songbirdspecies learn only a single song in their lifetime4. How sexual selection drivesthe evolution of single-song repertoires is not known. Here, by applyingdimensionality-reduction techniques to the singing behaviour of zebra finches(Taeniopygia guttata), we show that syllablespread in low-dimensional feature space explains how single songs function as honestindicators of fitness. We find that this Gestalt measure of behaviour captures thespectrotemporal distinctiveness of song syllables in zebra finches; that femalesstrongly prefer songs that occupy more latent space; and that matching path lengthsin low-dimensional space is difficult for young males. Our findings clarify howsimple vocal repertoires may have evolved in songbirds and indicate divergentstrategies for how sexual selection can shape vocal learning.
