Quantification of unusual carotenoid coloration in a male Common Rosefinch Carpodacus erythrinus

The red plumage coloration in birds, derived from the metabolic transformation of dietary yellow carotenoids, is thought to be influenced by both environmental conditions and individual body conditions. Here, we document the first recorded case of a Common Rosefinch ( Carpodacus erythrinus ) exhibiting extreme yellow plumage and quantify its coloration using reflectance spectrometry and Raman spectrometry. We compared this unique plumage with the typical range observed in adult males, which spans shades of red to orange and occasionally includes pale yellow patches. Our study revealed distinct differences in reflectance curves and Raman peak wavenumbers between the yellow feathers of the study individual and those of typical plumage. We deliberated upon several potential explanations for this pronounced yellow coloration, described for the first time in this species: 1) Disruption of keto-carotenoid production by genetic mutation; 2) dietary carotenoid limitation in the birds’ habitat which results in significant but potentially temporary yellow plumage within annual coloration fluctuations; 3) a lack of strong sexual selection for red coloration in this species. Further observations and investigations are needed to evaluate the ecological and physiological bases of color expression in the Common Rosefinch.