Building Complexity From Simplicity: A Songbird's Vocal Repertoire Varies Among Populations Despite Similarity of Syllables

Vocal communication plays a critical role in understanding animal behavior, evolution, and cognition. We developed an automated system combining audio signal processing and machine learning (supervised and unsupervised) to characterize the vocal repertoire of the White Spectacled Bulbul (<i>Pycnonotus xanthopygos</i>), a widespread passerine in Israel known for its complex year-round vocal activity. Analyzing hundreds of field recordings using passive acoustic monitoring (PAM), our system identified thousands of calls, revealing a hierarchically structured vocal repertoire composed of distinct complex vocalizations (<i>motifs</i>) and base units (<i>syllables</i>). Our results show that different populations possess unique motif repertoires, primarily consisting of population-specific motifs built from syllables that are similar across genetically distinct populations. This study enhances our understanding of this understudied species and highlights the White Spectacled Bulbul's potential as a model organism for investigating vocal communication and social learning in animals.