Temporal Dynamics of Dialects in the Whistled Songs of Starlings
Résumé
Previous studies revealed that whistled songs of starlings can be separated into different categories, among which five themes are found in the repertoires of all (or most) individuals. These “specific” themes show local variations but the different themes have different sizes of dialect areas.
This study investigates the temporal evolution of this complex dialectal system. Observations were made in an area where dialects were mapped three years earlier. They reveal an obvious temporal evolution of dialects, although the degree of variation differs according to the theme.
No structural change was observed for two themes (CC and ST), but some temporal dynamics in their dialect boundaries did appear. There were changes in the structures and boundaries of two other themes (IT and HT). However, they showed:
— a relationship between new and old structures, either with persistence of the old variants or with an apparent drift. Almost no really new structures were observed.
— all the 1980 variants recorded in 1983 were found at sites not far from the original one. The main changes consisted of extensions or regressions of variants along boundaries.
Lastly, the temporal evolution of RT dialects is unusual in that the changes are more sudden.
The variants have been replaced by different ones in some cases, but in others they have remained stable.
The complexity of the dialectal system is persistent on a temporal level, varying from stability for ST to sudden changes for RT, with IT and HT intermediate.