Humans but not Budgerigars ( Melopsittacus undulatus ) Consistently Prefer Sounds with Clear Harmonic Spectra

Comparing parallels between species that share music-like abilities with humans can illuminate and reveal selective pressures that shaped the origins of music. For instance, human vocalizations feature clear (i.e., unobscured by noise) harmonic-rich sounds. Our goal was to empirically test whether these features play into our aesthetic sense and how we structure music. We tested the vocal similarity hypothesis, which predicts that species prefer sounds resembling their own vocalizations, by comparing ourselves to budgerigars, a small parrot species that, like humans, can imitate sounds and detect and synchronize to acoustic rhythms. We hypothesized budgerigars and humans would favor noisy and clear timbres, respectively, because of each species’ vocalization structure. Using a place preference paradigm, we measured preferences for noisy sounds, clear sounds, and silence. While budgerigars, surprisingly, showed ambiguous preferences, humans consistently preferred clear sounds, as predicted. These results, along with further acoustic analyses, suggest that preference may result from an interplay of factors beyond vocal similarity, with known cross-species acoustic correlates of arousal, harmonic richness, and vocal culture as potentially driving factors. Our results support hypotheses about functional contexts in which human musicality evolved, such as social bonding via merging of the individual voices through harmonic-based synchronization during simultaneous vocalizations.