What correlation is absent in British breeding populations concerning wing length morphology?

Correlation between latitude and mean wing length for either sex.

The data from Britain highlights a major difference in population structure compared to the situation in Scandinavia. In Central Scandinavia, the migratory divide is fundamentally latitudinal, separating birds heading southwest from those heading southeast, leading to distinct wintering grounds. In contrast, within the British Isles, ringing data revealed no statistically significant relationship between the latitude where the birds bred and their average wing length, regardless of whether the data was analyzed for males or females. This lack of a latitudinal cline in Britain is significant because it contrasts with the clear latitudinal structuring seen in the migratory patterns across the Baltic region. This suggests that in Britain, selection pressures might be more localized, or that strong gene flow is effectively homogenizing any latent latitudinal morphological structure that might otherwise develop.