Nondestructive Raman spectroscopy confirms carotenoid-pigmented plumage in the Pink-headed Duck

Abstract

A small group of pigment classes is responsible for the wide range of plumage colors in modern birds. Yellow, pink, and other “warm” feather colors of many species are attributed to carotenoid pigments, a plumage trait that has an uneven distribution across modern bird species. Carotenoid plumage pigments are especially rare among fowl (superorder Galloanseres), and until recently, the Pink-eared Duck (Malacorhynchus membranaceus) from Australia provided the only evidence that any species of waterfowl (order Anseriformes) exhibits carotenoid-pigmented plumage. We analyzed a Pink-headed Duck (Rhodonessa caryophyllacea) study skin using Raman spectroscopy, without plucking or otherwise damaging the specimen. Raman spectra confirmed that the pink feathers of Rhodonessa are pigmented with carotenoids. Spectra from Rhodonessa were similar to those from Malacorhynchus, which suggests that the same carotenoid is the primary plumage pigment in both species. Moreover, spectra from Rhodonessa were similar to spectra from other taxa pigmented with ketocarotenoids. Malacorhynchus and Rhodonessa are distant relatives within Anseriformes, so these findings indicate multiple evolutionary origins of plumage carotenoids within the waterfowl or (less likely) many losses of plumage carotenoids from duck species. Our results show that pigment chemistry can be studied in precious ornithological specimens without damaging the specimens, and provide new evidence that the (apparently extinct) Rhodonessa possessed what is evolutionarily an extremely rare trait among waterfowl.