Large-scale geographic variation in iridescent structural ornaments of a long-distance migratory bird
Résumé
Iridescent colours produced during moult likely play an important role in pair formation in birds. We sought to quantify geographic variation in such colouration in a duck species, Eurasian teal Anas crecca , in winter (when mating occurs) to evaluate whether this variation refl ects birds ' breeding origins or diff erential individual migration strategies in both males and females. We combined information on feather production region and individual attributes (body size, sex and age) of Eurasian teal from 82 wintering sites in France. Feather production region (moult site or natal origin) was inferred using feather deuterium values ( δ D f ). We performed spectral measurements to evaluate speculum colour and brightness contrasts for 1052 teal collected over four years. Colouration diff ered strongly among wintering regions, with birds wintering in eastern France exhibiting higher colour contrast than those wintering in the west. Body size and colouration were positively related. Th ere were no diff erences in cohort-specifi c δ D f values between separate wintering regions in France, indicating that within a winter quarter teal originated from areas across the entire breeding range. Overall, patterns of spatial variation in feather colouration were related most closely to body size which was consistent with predictions of a diff erential migration hypothesis, with larger and more colour-contrasting birds wintering closer to their breeding grounds. Because moult speed is also known to aff ect colour production, early breeders or individuals that skipped reproduction may have invested more or earlier in their feather quality to gain potential advantages in monopolizing future mates.