A review of the distribution of Yellowhammer (Emberiza citrinella) dialects in Europe reveals the lack of a clear macrogeographic pattern

Abstract

The Yellowhammer (Emberiza citrinella) is a bird with a very long history of research in geographic song variation, dating back to the 1920s. Numerous features make the Yellowhammer a suitable model for studying songbird dialects: it is a common and easily recognizable species, has a simple song, keeps singing long into the season, and has dialects (defined by the final song phrase) that are relatively easy to identify. Numerous works have focused on Yellowhammer dialects and their geographic distribution in various parts of Europe, often revealing mosaic-like patterns even at relatively restricted spatial scales. However, it has been repeatedly suggested that Yellowhammer dialects can be divided into two groups showing a macrogeographic pattern of distribution (in some recent works, eastern and western groups of dialects have been mentioned). To evaluate this assumption, data scattered in various published sources need to be pooled. Comparing historical records is nevertheless challenging, as various nomenclatures for Yellowhammer dialects were used until the mid-1980s (when a detailed system coined by Poul Hansen in Denmark was adopted), and older studies often did not differentiate between dialects recognized at present. To facilitate further work on song variation of this species, we summarized published information on the distribution of Yellowhammer dialects in Europe, added data from recordings publicly available online and in selected sound collections, and unified the different dialect nomenclatures used in the past. We demonstrate that the continental-wide distribution patterns of Yellowhammer dialects do not support the existence of broad, geographically distinct dialect groups (eastern vs. western). Furthermore, some of the presently recognized distinct dialect types seem to be parts of a broader continuum. Based on our conclusions, we discuss potential future avenues for Yellowhammer dialect research.