Sunday, January 21, 2018

[Ornithology • 2018] Structural Absorption by Barbule Microstructures of Super Black Bird of Paradise Feathers


Magnificent Riflebird Ptiloris magnificus during courtship display.


in  McCoy, Feo, Harvey & Prum, 2018.
photo: Tim Laman || 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.

Magnificent Riflebird Bird of Paradise Ptiloris magnificus male displaying to female.
 photo: Tim Laman

Fig. 1  Six species of birds of paradise and one close relative.
a, b Species with normal black plumage patches. cg Species with super black plumage patches.

a Paradise-crow Lycocorax pyrrhopterus. b Lesser Melampitta Melampitta lugubris, a Papuan corvoid closely related to birds of paradise.
c Princess Stephanie’s Astrapia Astrapia stephaniae. d Twelve-wired Birds-of-Paradise Seleucidis melanoleucus. e Paradise Riflebird Ptiloris paradiseus during courtship display. f Wahnes’ Parotia Parotia wahnesi. g Superb Bird-of-Paradise Lophorina superba during courtship display with female (brown plumage).

Photos: a @Hanom Bashari/Burung Indonesia; b Daniel López-Velasco; c Trans Niugini Tours; d–f Tim Laman; g Ed Scholes.  DOI:  10.1038/s41467-017-02088-w 

Fig. 3 Examples of normal and super black feather microstructure.
 a SEM micrograph of Lycocorax pyrrhopterus normal black feather with typical barbule morphology; scale bar, 200 µm. b SEM micrograph of Parotia wahnesi super black feather with modified barbule arrays; scale bar, 50 µm. c Gold sputter-coated normal black breast feather of Melampitta lugubris appears gold. d Gold sputter-coated super black breast feather of Ptiloris paradiseus retains a black appearance indicating structural absorption. SEM stubs are 12.8 mm in diameter.

A comparison of a normal feather, top left, and a feather from a paradise riflebird, top right.
The bottom panels are the feathers coated in gold. Notice how the riflebird’s still appears a deep black.
photos: Dakota McCoy 


Dakota E. McCoy, Teresa Feo, Todd Alan Harvey and Richard O. Prum. 2018. Structural Absorption by Barbule Microstructures of Super Black Bird of Paradise Feathers. Nature Communications. 9, Article number: 1. DOI:  10.1038/s41467-017-02088-w

Evolved illusion: Blackest black gives bird of paradise an edge  news.yale.edu/2018/01/09/evolved-illusion-blackest-black-gives-bird-paradise-edge

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