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Composition and sequential organization of song repertoires in Cassin’s Vireo (Vireo cassinii)

Hedley, Richard W.
Journal of ornithology 2016 v.157 no.1 pp. 13-22
birds, phylogeny, vocalization, Sierra Nevada (California)
The rules governing bird song sequences vary considerably across the avian phylogeny, and modifications to these rules represent one of the many ways in which bird song varies interspecifically. Cassin’s Vireo (Vireo cassinii) is one species that shows a highly structured syntax, with clearly non-random patterns of sequential organization in their songs. Here I present a description of Cassin’s Vireo song sequences from the Sierra Nevada Mountains in California and employ network analysis to quantify transition patterns within the songs. Repertoire sizes varied between 44 and 60 phrase types per bird for the 13 birds analyzed here. The repertoire was subdivided into ‘themes’ containing between two and seven phrase types. The birds sang the phrase types in a given theme for a time before eventually introducing a new theme; in this manner the repertoire was revealed relatively slowly over time. Theme composition within a bird’s repertoire did not change within or between singing bouts throughout the season. The tendency to sing in themes was corroborated by network analysis, which revealed small-world structure in the songs. Phrase types were widely shared within the population. I discuss these findings as they compare with the singing styles of other species, both closely and distantly related.