Detailed large-scale mapping of geographical variation of Yellowhammer Emberiza citrinella song dialects in a citizen science project

Song dialects, as a special case of geographical variation in vocalization, are useful tools in the study of a number of topics ranging from cultural evolution to the emergence of reproductive barriers, and thus continue to be the focus of many bird-song studies. The Yellowhammer Emberiza citrinella is a common Palaearctic bird with a long breeding season and song period, whose distinctive song exhibits clearly distinguishable dialects differing in the composition of the final phrase. The species is therefore particularly suitable for large-scale studies of dialect distribution involving not only experts but also members of the public. Here we demonstrate that citizen science can indeed allow mapping of songbird dialect distribution on a national scale in unprecedented detail. During the project Dialects of Czech Yellowhammers, which collected almost 4000 recordings over 6 years (2011-2016), we obtained information on dialect distribution for almost 90% of the territory of Czechia. We detected most of the common dialect types known elsewhere in Europe, and these were distributed in a fragmented fashion, with several unusual and rare dialects also detected in small areas. However, the highly scattered distribution of birds using some final phrases traditionally assigned to distinct dialects suggests that classification of Yellowhammer dialects warrants a thorough re-assessment based on quantitative data. Successful involvement of the public in this and other ongoing citizen science projects has contributed to the establishment of the Yellowhammer as a model species for dialect research. The dataset will serve as a foundation for future studies investigating processes responsible for the origin and maintenance of avian dialects, and may be particularly useful for evaluating their spatial and temporal stability.