Are blackcaps sylvia atricapilla differential distance migrants by sex?

Aims: To investigate if male and female blackcaps show differences in the amplitude of migratory movements. Methods: The extent of movements of male and female British blackcaps were analysed using ringing recovery records. Furthermore, through a literature review and the collection of original field data, the sex-ratios of blackcap samples taken at several latitudes in Europe and Africa were compared. Results: There were no differences between British male and female blackcaps in relation to wintering latitude or distance moved during migration. Sex-ratios of blackcap samples were quite even across a wide range of latitudes. However, there was a significantly larger proportion of females in samples of birds that wintered in Africa. Conclusions: Laboratory data and morphological studies have yielded inconclusive results in relation to the question of whether or not European blackcaps are differential distance migrants. The results from the present study suggest that British blackcaps are not differential distance migrants. Furthermore, there is, at best, only a weak latitudinal segregation of the sexes of blackcaps wintering in Europe and Africa. The slightly higher proportion of males in European samples, when compared to Africa, could result from a differential behaviour of males and females in some blackcap populations, or simply result from differences in the sex-ratios of blackcap populations breeding and wintering in different areas. An absence of a pronounced latitudinal segregation in the size-monomorphic blackcap is interesting, and contrasts with the pattern found in more sexually dimorphic species, such as the chiffchaff Phylloscopus collybita or the robin Erithacus rubecula