Octave equivalence perception is not linked to vocal mimicry: budgerigars fail standardized operant tests for octave equivalence

Octave equivalence describes the perceived similarity of notes separated by an octave or a doubling in frequency. In humans, octave equivalence perception is used in vocal learning, enabling young children to approximate adult sounds where the pitch lies outside of their vocal range. This makes sense because the octave is also the first harmonic of any tonal sound including the human voice. We hypothesized that non-human animals may also need octave equivalence perception in vocal mimicry, the copying of other species or environmental sounds, to approximate sounds where the pitch lies outside their vocal range. Thus, in the current study, we tested budgerigars (Melopsittacus undulatus), a vocal mimicking species, for octave equivalence perception. Budgerigars were trained and tested in a go/no-go operant task previously verified in humans. Budgerigars did not show evidence of octave equivalence perception. This result suggests that vocal-mimicking does not necessarily facilitate or presuppose octave equivalence perception.