Song Conformity and Continuity in Song Dialects of Redwings Turdus iliacus and Some Ecological Correlates

Abstract

This study is based on the assumption that song sharing in neighbouring Redwings is advantageous in terms of genetic fitness. By calculating dispersal and immigration rates we also wanted to gain information about the timing of song learning and the causal background for the maintenance of local song dialects in this species. We recorded and analysed the song patterns of 304 Redwing males during three or four consecutive years in six populations in central Norway and Sweden. Data on breeding success, dispersal and immigration were collected for three of the populations. Although some males had two song types, most had only one. The frequency of two-type singers in the different areas did not correlate with the density of singing or breeding birds, nor with the extent of song sharing between birds, which differed considerably between areas. Song sharing did not correlate with the density of singing or breeding birds, but was positively correlated with breeding success. To explain this relationship we suggest that differences in age structure, onset of breeding in spring and nest predation are important. Sparsely populated areas and areas with high breeding success had a more stable song pattern from one year to the next than areas with higher density and lower breeding success, respectively. Colour-banding indicated that on average 17% of adults returned to the area in which they nested previously, whereas less than 1% of nestlings returned to the natal area. Thus, we suggest that the local nestling population contributed very little to the same breeding population in the following year, and that the longterm maintenance of a local dialect may be explained by the young males copying the song of the older males of the area in which they settle to breed in their first spring.