Geographically well-distributed citizen science data reveals range-wide variation in the chipping sparrow's simple song

Abstract

Geographical variation has been widely studied in oscine songbirds, with particular attention paid to the interplay between variables associated with learned song and dispersal. While most field-based studies have focused on discrete dialects, analysing data from quickly growing citizen science libraries could uncover geographical patterns in species previously thought to exhibit random variation in song. Specifically, using citizen science birdsong databases, we test whether chipping sparrow, Spizella passerina, song is geographically structured on a continental scale. The chipping sparrow is a particularly well-suited species for this study, since individuals have a simple song of one repeated syllable, have only the beginning of their first breeding season to adjust their song before crystallization and have been shown to match their song to a nearby neighbour while establishing their first territory. If most chipping sparrows adopt a neighbour-matching strategy, we might expect local syllable similarity; in contrast, field studies have shown that local syllable diversity has been maintained over time. We analyse 820 individual recordings of the simple, yet diverse, song of chipping sparrows to assess whether long-range geographical patterns have formed despite this local song variation. We found significant correlations between song features and geographical distance, associated with longitude but not latitude: chipping sparrows in the eastern United States and Canada sing at a slower rate (fewer, longer syllables) than the western population. However, comparing individual syllable types between regions, we found diverse song types persist across this species’ range. To better contextualize our findings, we re-evaluate available genetic sequences of chipping sparrows to test for genetic differentiation between the eastern and western populations in which we found song differences. Our results suggest that there are two culturally distinct subpopulations of migratory chipping sparrows that are genetically indistinguishable using mitochondrial DNA, motivating future studies on migration patterns and additional sequencing of nuclear DNA.