Structural absorption by barbule microstructures of super black bird of paradise feathers

Dakota E Mccoy,Teresa Feo,Todd Alan Harvey,Richard O Prum

doi:10.1038/s41467-017-02088-w

Abstract

Many studies have shown how pigments and internal nanostructures generate color in nature. External surface structures can also influence appearance, such as by causing multiple scattering of light (structural absorption) to produce a velvety, super black appearance. Here we show that feathers from five species of birds of paradise (Aves: Paradisaeidae) structurally absorb incident light to produce extremely low-reflectance, super black plumages. Directional reflectance of these feathers (0.05–0.31%) approaches that of man-made ultra-absorbent materials. SEM, nano-CT, and ray-tracing simulations show that super black feathers have titled arrays of highly modified barbules, which cause more multiple scattering, resulting in more structural absorption, than normal black feathers. Super black feathers have an extreme directional reflectance bias and appear darkest when viewed from the distal direction. We hypothesize that structurally absorbing, super black plumage evolved through sensory bias to enhance the perceived brilliance of adjacent color patches during courtship display.

Highlights

Many studies have shown how pigments and internal nanostructures generate color in nature
We visually selected five species of polygynous birds of paradise with profoundly black plumage from five different genera—Ptiloris paradiseus, Seleucidis melanoleucus, Astrapia stephaniae, Lophorina superba, and Parotia wahnesi— and two species with normal black plumage—Lycocorax pyrrhopterus and Melampitta lugubris—to serve as comparative controls (Supplementary Table 1)
These results demonstrate that the modified barbule arrays of super black feathers increase multiple scattering of light, and contribute to a darker appearance through increased structural absorption, relative to the typical barbule morphology of normal black feathers

Summary

Introduction

Many studies have shown how pigments and internal nanostructures generate color in nature. We show that feathers from five species of birds of paradise (Aves: Paradisaeidae) structurally absorb incident light to produce extremely low-reflectance, super black plumages. Directional reflectance of these feathers (0.05–0.31%) approaches that of man-made ultraabsorbent materials. SEM, nano-CT, and ray-tracing simulations show that super black feathers have titled arrays of highly modified barbules, which cause more multiple scattering, resulting in more structural absorption, than normal black feathers. We hypothesize that structurally absorbing, super black plumage evolved through sensory bias to enhance the perceived brilliance of adjacent color patches during courtship display. By increasing the number of times light scatters, structurally absorbing materials can increase total light absorption to produce a profoundly black appearance. We hypothesize that these feathers evolved to enhance the perceived brilliance of adjacent color patches by generating an optical/sensory illusion during mating displays

Methods

Results

Conclusion