Acquired human speech sounds replace conspecific syllables in the song of Budgerigars Melopsittacus undulatus.

The psittacine budgerigar Melopsittacus undulatus, a parrot species known to be a vocal learner, produces long and complex songs composed of different syllable types. Budgerigars can imitate heterospecific sounds as new song syllables, including human speech, but it is unclear how the imitative sounds affect the proportion of different syllables or high-order song structure, such as temporal pattern, which is characteristic of the budgerigar song. We analyzed recordings of songs from six adult male budgerigars with or without imitations of Japanese words to identify whether songs with imitations differed in structure from those without imitations. Songs with imitations contained significantly fewer narrowband syllables and more harmonic syllables, including imitative vocalizations, than those with no imitations. On the other hand, there were no significant differences in most of the temporal parameters between songs with and without imitations, suggesting that the high-order song structure was less affected by incorporating newly acquired syllables. These observations suggest that the heterospecific imitations replaced the conspecific narrowband syllables, which are frequently seen in normal budgerigar song and are acquired through learning processes, possibly without changing the temporal pattern in the song of budgerigars.