Song Dialects of White-Crowned Sparrows: Historical Processes Inferred from Patterns of Geographic Variation

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Abstract
Geographic variation in the syllabic structure of the song of white-crowned sparrows (Z. l. nuttalli) resident in coastal California [USA] are described. Six large and relatively homogenous populations that differed discretely at 1 locus in the song, the complex syllable, were identified and named dialect populations. Two superdialects were also identified on the basis of 3 other loci in the song, the introduction and the ending. Using another part of the song, the simple syllable locus, large-scale geographic clusters of similarity that were moderately concordant with dialect variation were also identified. From the patterns of geographic variation shown by the 4 song loci, the study area was colonized by 2 ancestral populations. The existing song populations are therefore interpreted to be in secondary contact. Relatively narrow zones of overlap at dialect borders are identified and their widths estimated. Application of cline theory to the data suggests that 100-200 yr have elapsed since secondary contact.