Divergence of vocal culture among isolated alpine habitats is inconsistent among three Oscine species

Abstract

Divergence in song culture has been well documented among isolated bird populations. Montane populations separated by unsuitable lower-elevation habitats thus appear to be excellent candidates for cultural divergence, and existing data support this conjecture. To explore the generality of this phenomenon, we investigated song sharing patterns in songbird species breeding in isolated alpine life zones in the Rocky Mountains of Colorado. We recorded songs of American Pipits (Anthus rubescens alticola), Wilson’s Warblers (Cardellina pusilla pileolata), and White-crowned Sparrows (Zonotrichia leucophrys leucophrys) across 19 sites among 6 mountain ranges. We used spectrographic cross-correlation to calculate song similarity coefficients between individuals within and among populations. White-crowned Sparrows exhibited significantly elevated song sharing within isolated mountain ranges, but Wilson’s Warbler and the American Pipit did not. Cluster analyses showed that White-crowned Sparrow songs diverged among alpine fragments but were generally similar among sites within contiguous alpine habitat within mountain ranges. There was no such clustering within American Pipit or Wilson’s Warbler populations. Song similarity declined with distance between sites within contiguous alpine habitat in White-crowned Sparrows but not in American Pipits or Wilson’s Warblers. Our results provide convincing evidence for the existence of geographically structured vocal culture in White-crowned Sparrow populations in Colorado, and this geographic pattern may be explained by clinal variation rather than by a mosaic pattern of divergence among isolated alpine fragments.