Variation in quantitative properties of song among European populations of reed bunting (Emberiza schoeniclus) with respect to bill morphology

We analysed the geographical variation in quantitative song properties among reed bunting populations belonging to two subspecies groups with different bill morphologies: large and curved (namely E. s. intermedia and witherbyi, in southern Europe) and thin and conical (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 high individual variation. Populations with similar morphology were more homogeneous in song characters, despite geographical distances between them. The two subspecies groups differed mainly in number of different syllable types used in a song, the southern group having higher syllable complexity. Cluster analysis and matrix correlation tests showed an association between song variation and morphological variation. The populations morphologically belonging to 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 socially learned, populations mixing in winter and, along the contact zone, populations of different subspecies group often breeding a few km apart. The generally high 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 a rapid cultural evolution of song in this species.

Population memetic analysis of variation of song, geographical distribution and bill morphology in the reed bunting

We applied population memetic models to the analysis of cultural variation among 11 European reed bunting populations belonging to two subspecies groups differing in bill morphology. We tested whether patterns of meme diversity within and among populations and between the two subspecies groups correspond to patterns of variation in bill morphology. Within-population meme diversity was high and the degree of memetic divergence within groups was significant and higher among southern thick billed populations than among northern thin billed populations. There was, however, no significant memetic difference between the two subspecies groups. Tests of correlation between all groups indicated that memetic variation is associated with geographical distance and not with morphological variation. The results suggest a demographic structure of reed bunting populations similar to that of island populations of other bird species. The lack of memetic differences between them indicates that populations are not culturally isolated, despite the morphological, ecological and genetic differences. We discuss possible evolutionary explanations of the patterns of variation found.

Responses to playback of different subspecies songs in the reed bunting

Populations of reed buntings in the western Palearctic are classified in two major subspecies groups according to morphology: northern migratory schoeniclus and Mediterranean resident intermedia. Songs of the two groups differ mainly in complexity and syllable structure, with intermedia songs being more complex. We explored the possibilities of song as a subspecies isolating mechanism by testing if male schoeniclus Reed Buntings reacted differently to field playbacks of songs from their own subspecies group, from the foreign subspecies group and from a control species, the yellowhammer Emberiza citrinella. We tested 30 different males, each with a different song belonging to one of the three categories: own, foreign and yellowhammer. Unlike songs of the two subspecies groups, Yellowhammer song elicited no response. Differences between reactions to own and foreign subspecies group songs were not significant, even though differences in response type (singing vs approaching) suggested some degree of uncertainty in classification of foreign song. We conclude from these results that the subspecies may be only in the first stages of the isolation process.

The geographical distribution of populations of the large-billed subspecies of reed bunting matches that of its main winter food

We investigated the potential effects of ecological selection on the population structure and distribution of a polytypic bird species. We compared the presence of insect remains (mainly dormant larvae) in the winter diet of two reed bunting morphs, small billed schoeniclus and large billed intermedia and studied the distribution of this resource within reed stems in seven north Italian localities where the two morphs breed (3 schoeniclus and 4 intermedia populations). We then tested if the distributions of winter insect resources and breeding populations of the large bill morph overlapped. The winter diets of the two morphs were significantly different in terms of frequency of insect remains. The distribution of the larvae in reed stems matched closely the distribution of large billed breeding populations. These results, when compared to theoretical models of parapatric distribution, suggest that the two morphs may be subject to ecological (vicariant) selection maintaining their reproductive isolation.