Meeting Abstract
Considerable progress has been made in our understanding of how pigments and nanostructures within the feather contribute to plumage coloration. However, external surface structures can also significantly impact visual appearance, such as when surface structures cause multiple scattering of light, leading to nearly complete, incremental absorption of light or “structural absorption”. Structural absorption by super black materials is of great interest to materials science due to a wide variety of technological applications. Biological examples of structural absorption have been previously discovered in butterfly and snake scales. Here, we show that feathers from 5 species of birds of paradise (Aves: Paradisaeidae) structurally absorb incident light to produce extremely low-reflectance, super black plumages. Directional reflectance of super black feathers were one or two orders of magnitude less than normal black feathers. SEM and nano-CT revealed highly modified barbules in super black feathers. Ray tracing simulations using 3D tomographic models of feather surfaces confirm that the modified barbule morphology of super black feathers cause more multiple scattering of light, resulting in more structural absorption, than normal black feathers. Furthermore, super black feathers exhibited extreme directional bias in reflectance such that they always appear darkest when viewed from a specific direction. We hypothesize that structurally absorbing super black plumage evolved to enhance the perceived brilliance of adjacent color patches during male courtship display.
