Individual-specific associations between warble song notes and body movements in budgerigar courtship displays.

Complex behavioral sequences such as courtship displays are often multimodal, and coordination between modalities is critically important. In learned and variable behavioral sequences such as songs, individual variability may also extend to multimodal coordination and the associations between modalities. However, individual variability in complex multimodal sequences and in coordination between distinct behaviors remains underexplored. Here, we report that budgerigars, which continuously learn and modify their complex warble songs, exhibit associations between body movements and song notes during courtship. Some associations are unique to individuals, and others are universal across individuals. Additionally, some individuals exhibit more unique associations than others. We also find that birds warbling in the absence of body movements emit all notes with broadly similar odds ratios. Our data suggests a hierarchy of associations, some individual-specific and others common to all individuals, between body movements and songs. We propose that these associations may be learnt and modified through social interactions, resulting in individual variability.

Higher-order dialectic variation and syntactic convergence in the complex warble song of budgerigars.

Dialectic signatures in animal acoustic signals are key in the identification of and association with group members. Complex vocal sequences may also convey information about behavioral state, and may thus vary according to social environment. Some bird species, such as psittaciforms, learn and modify their complex acoustic signals throughout their lives. However, the structure and function of vocal sequences in open-ended vocal learners remains understudied. Here, we examined vocal sequence variation in the warble song of budgerigars, and how these change upon contact between social groups. Budgerigars are open-ended vocal learners which exhibit fission-fusion flock dynamics in the wild. We found that two captive colonies of budgerigars exhibited colony-specific differences in the syntactic structure of their vocal sequences. Individuals from the two colonies differed in the propensity to repeat certain note types, forming repetitive motifs which served as higher-order signatures of colony identity. When the two groups were brought into contact, their vocal sequences converged, and these colony-specific repetitive patterns disappeared, with males from both erstwhile colonies now producing similar sequences with similar syntactic structure. We present data suggesting that the higher-order temporal arrangement of notes/vocal units is modified throughout life by social learning as groups of birds continually associate and dissociate. Our study sheds light on the importance of examining signal structure at multiple levels of organization, and the potential for psittaciform birds as model systems to examine the influence of learning and social environment on acoustic signals.