Bachman's Sparrows (Peucaea aestivalis) have unusually large song repertoires for New World sparrows. Answering questions about their function, evolution, and development requires thorough description of these repertoires in multiple populations. Here, we quantified repertoire size, song type sharing, and sequence sharing—specifically, the sharing of preferred song type transitions—of primary songs within each of 2 populations of Bachman's Sparrows at northeastern and southeastern ends of the species' breeding range. We recorded 20 males in southern North Carolina (NC) and 18 males in eastern Florida (FL). Individual repertoire size had a mean of 48–49 song types in both populations. Within each population, males shared many song types, with 80% repertoire overlap between any 2 males in NC and 49% in FL. This within-population song sharing was independent of distance between males' territories. The sequence in which males sang song types was neither stereotyped nor random, and within each population, preferred song transitions were shared by all (NC) or most (FL) pairs of males. The sharing of preferred song transitions was also not correlated with the distance between territories, suggesting that birds do not adjust repertoires or song sequences in adulthood to match more closely those of territory neighbors. The function and ontogeny of the repertoire features documented here in Bachman's Sparrows—large repertoires with high sharing of both song types and preferred song transitions—invite further study.

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