Origin-related differences in plumage coloration within an island population of great tits (Parus major)

Several studies have described geographic variation in plumage coloration, providing important insights into the processes of local adaptation and speciation. Given that such variation appears to be common, individuals of different origin within a single population may vary accordingly. However, as yet no study has been able to test for such origin-related differences. The population of great tits (Parus major L., 1758) on the small Dutch island of Vlieland is especially suitable for such a study, as we know of every breeding adult whether it has been born on the island or not, and if it is, where on the island it was born. Furthermore, we have previously found large differences in clutch size and survival among birds of different origin in the same population. Here, we measured the spectral reflectance of the yellow breast feathers, and found that yearling, but not older, birds born in the eastern part of the island had feathers that were of a less bright yellow and UV than birds born elsewhere, irrespective of where they were breeding. Interestingly, this difference in coloration among yearlings of different origin shows a remarkable similarity with the genetic differences found earlier in this population with respect to clutch size and local survival. We thus show that systematic differences in color signals may exist within populations, among individuals of different origin, and we argue that it is crucial that such variation and its potential implications be accounted for irrespective of whether these differences have a genetic or an environmental basis.