Novel Approach to Inter-Onset-Interval Ratio Uncovers Music-Like Rhythmic Patterns in Budgerigar (Melopsittacus undulatus) Warble Song.

Rhythm is an essential part of human music. Recently, there has been a surge of interest in the production of rhythmicity in nonhuman animal vocalizations. Novel methods have found widespread rhythmic behaviors-including those with music-like properties-among nonhuman animals. Parrots appear to be uniquely flexible and self-motivated in engaging with rhythmic structures. Previous work has found evidence supporting rhythmic capabilities in the budgerigar, a small parrot; however, little is known about rhythmicity in their natural behavioral repertoire thus far. As such, we investigated the rhythmic structure of their complex learned warble song, developing an adapted statistical approach that addresses assumptions/biases found in other methods. After validating this method using human speech and song data, we found nonrandom and structured rhythmicity in the budgerigar warble song that shows similarities in rhythmicity to human music. We also identified two warble element pairs that seem to be essential for producing these budgerigar rhythms. The grouped rhythmic distributions observed in budgerigars appear to arise from different individual strategies, with differing uses of these element pairs among male individuals. These results, combined with earlier work, suggest that rhythmicity is an important aspect of budgerigar communication.