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

Abstract

Dialectic signatures in animal acoustic signals are key in identification and association with group members. Complex vocal sequences may also convey information about behavioral state, and may thus vary according to social environment. Many bird species learn and modify their complex acoustic signals throughout their lives. However, the structure and function of vocal sequences in perennial 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 perennial 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 within months of contact, and these colony-specific repetitive patterns disappeared, with males from both erstwhile colonies now producing similar sequences with similar syntactic structure. Our data suggests that budgerigars can encode substantial information in the higher-order temporal arrangement of notes/vocal units, which 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 organisation, and the potential for psittaciform birds as model systems to examine the influence of learning and social environment on acoustic signals.