We analysed the geographical variation in quantitative song properties among reed bunting (Emberiza schoeniclus ssp.) populations belonging to two subspecies groups with different bill morphologies: large and curved bill (namely E. s. intermedia and E. s. witherbyi, in southern Europe) and thin and conical bill (E. s. schoeniclus, in northern Europe). We collected song recordings from 11 European populations of the two subspecies groups and measured song properties of 116 males. We found significant differences among populations despite a high degree of individual variation. Populations with similar morphology were more homogeneous in song characters, despite geographical distances between them. The two subspecies groups differed mainly in the number of different syllable types used in a song, with the songs of the southern group having higher syllabic complexity. Cluster analysis and matrix correlation tests showed an association between song variation and morphological variation. The populations morphologically belonging to E. s. schoeniclus along the contact zone of the breeding distributions had song characters similar to southern populations and possibly represent a "hybrid" zone, which is not evidenced by morphological or recent genetic analyses. This may be due to song being learned socially, populations mixing in winter and, along the contact zone, populations of different subspecies groups often breeding a few kilometres apart. The generally high degree of variation in song among populations can be a consequence of the relative isolation of the breeding populations, which are restricted to uncommon and fragmented habitats, along with the rapid cultural evolution of song in this species.
Phenotypic Divergence among West European Populations of Reed Bunting Emberiza schoeniclus: The Effects of Migratory and Foraging Behaviours
