The evolution and function of avian vocal sequences

Abstract

The elaborate acoustic signals of animals consist of multiple components or modules. These modules typically follow complex temporal arrangements, referred to as syntactic structure. Syntax of a vocal sequence can convey important information about species or group identity, as well as behavioral context. Here, we investigated both the evolutionary and mechanistic drivers of vocal sequence structure in two avian taxa - wren-babblers (Spelaeornis) and budgerigars (Melopsittacus undulatus). Using a robust computational analytic framework, we uncover evidence that diversification of song structure in Spelaeornis involves syntactic diversification without divergence of individual notes. Additionally, we also found that syntactic diversification occurs along geographic barriers, a pattern similar to human linguistic diversification in the region. To address the proximate functions of vocal sequences, we examined the influence of social environment and behavioral context on the syntactic structure of budgerigar warble song. We found that warble sequences do not differ across behavioral contexts. However, individuals from different colonies possess higher-order dialectic signatures of colony identity embedded in the temporal organization of warble notes. Colonies differed in the propensity to repeat certain note types, this serving as a signature of colony identity. This thesis research emphasizes the importance of examining evolutionary and mechanistic drivers of signal structure at multiple levels of signal organization, and the strength of robust analytic frameworks to examine higher-order patterns in animal vocal signals.