Constancy of basic pattern in the song of two populations of starlings : a comparison of song variation between sedentary and migratory populations
Résumé
The comparison of local song variations between a migratory and a sedentary population of starlings shows the species-specificity of the basic categories and of their variation range. Local variations were studied for different themes in the repertoire, near Kaiserslautern (West Germany) during the reproductive season of 1982. Results were compared with those previously obtained in Brittany (France). In the study area in Germany, 80 % of the individuals migrate in autumn whereas the Breton starlings remain near the colony all year. To compare the whistles of individuals of different regions, by examing the important variations in their frequency modulation, it is necessary to know the general basic features of the whistles. Using sonograms, the whistles of starlings can be divided into 8 general classes according to particular criteria: rhythmicity, modulation etc. Five themes, among these 8 classes, are sung by all or most of the individuals (“specific themes”).
The analyses of whistles give us the following results:
1 The songs of the migratory population studied in W. Germany contain basic features corresponding to those known in the sedentary French population.
2 Like the Breton starlings, those in Germany show a “theme-specific” dialect distribution: the rhythmic theme shows several variants in an area of a few km2, whereas the uniform simple theme presents only one variant over several 100 km2. For the five themes, the dialectal mosaic is totally different: two birds can have the same variant of one given theme and sing different dialects of another.
3 The themes which, in France, show a great number of variants over a small area present the same tendency towards strong subdivision in dialects in Germany.
In the two study areas, no correlation could be found between dialectal boundaries and ecological factors.
4 Considering that two starling populations with very different characteristics show such similarities in their basic song structures and also in their pattern of local variation (in the parameters concerned and in the sizes of the dialect areas) we may suppose that the basic structure of the specific themes could be determined by a genetic program. Some characteristics, like the precise details of the frequency modulation, may be due more to learning and may conform to the local dialect.