Humans, but not zebra finches, produce spontaneously isochronous song through the lifespan

Isochrony—the regular beat of a metronome—is cross-culturally ubiquitous in music. Is this ubiquity due to a widespread biological inclination for isochrony in acoustic communication? If so, it should be present in lesser-studied vocal music, in the absence of musical training and early in development, and in comparable non-human species' vocalizations. We quantified isochrony in improvised songs from non-musician adults ( n = 15, 24–82 years old) and children ( n = 38, 3–10 years old), and in songs from juvenile and adult zebra finches ( n = 77, ∼50 and >120 days post-hatch). Isochrony was expressed in Western non-musician and children's improvised songs to a comparable degree. In contrast, both juvenile and adult zebra finches produced songs with less isochrony than chance, with no evidence for the learning of isochrony. These data show that spontaneous isochrony in learned vocalizations appears differently in two species. We propose that species variation in chorusing behaviors may explain why.