Carminic Acid Based Red Dye from Scale Insects Detected in Red Ruby‐Crowned Kinglet Feathers by Surface‐Enhanced Raman Scattering

In most birds, red feather color is linked to diet and attributed to carotenoids contained in plants and fruits. In the red crown feathers of the Ruby-crowned Kinglet (Regulus calendula), a new biopigment was identified based on carminic acid, the main coloring compound of cochineal (Dactylopius coccus) and other scale insects. This has revealed a potential new class of carminic acid-based biopigments, not previously identified in feathers. In this research, red crown feathers of a Ruby-crowned Kinglet were analyzed by surface-enhanced Raman scattering (SERS) employing synthesized silver star-shaped colloids as the nanoplasmonic platform. Results indicated peaks at 450, 670, 1290-1312, 1355, 1410, 1570, 1620 cm-1 in the feather SERS spectra characteristic of carminic acid. SERS has proven to be an extremely sensitive, non-destructive technique for the identification of different feather biopigments, even at trace quantities and in the presence of other predominant coloring substances.