Measuring and modelling the reflectance spectra of male Swinhoe's pheasant feather barbules.

A range of iridescent colour appearances are presented by male Swinhoe's pheasants' (Lophura swinhoii) mantle feathers. Two distinct regions of the open pennaceous portion of its feathers display particularly conspicuous angle-dependent reflection. A bright blue band appears in one region at normal incidence that spatially shifts to another at higher illumination angles. The two-dimensional photonic crystal-like nanostructures inside the barbules of these two regions are similar. However, this study found that the spatial variation in their colour appearance results from a continuously changing orientation of barbules with respect to the alignment of their associated barb. A multi-layered rigorous coupled-wave analysis approach was used to model the reflections from the identified intra-barbule structures. Well-matched simulated and measured reflectance spectra, at both normal and oblique incidence, support our elucidation of the origin of the bird's distinctive feather colour appearance.