For anyone who is really curious the original article’s URL is here:
https://www.nature.com/articles/s41467-017-02088-w It looks like it’s an
open-access paper, so anyone should be able to view it at no cost. There’s a
photo of the gold-coated feather (that still looks black) at part of the
[mailto:bounce-122250313-3494...@list.cornell.edu] On Behalf Of Nari Mistry
Sent: Thursday, February 01, 2018 11:03 AM
Subject: [cayugabirds-l] Super-black feathers in Birds of Paradise
Curious readers may be interested in this evolutionary feature in Birds of
Paradise . I have extracted below some paragraphs from a report in PhysicsWorld
(UK). I don't have the reference to the original papers.
========================= Extracted from PhysicsWorld (UK)=====
Male birds of paradise have exceptionally black feathers and now researchers in
the US have explained how the feathers manage to reflect tiny amounts of light.
The team found that some feathers have complicated structures that create a
scattering effect that results in almost zero reflectance of light under
certain conditions – giving them a “super-black” appearance. The researchers
think that this black plumage evolved to enhance the perceived brilliance of
adjacent colour patches during courtship displays.
Birds of paradise are found in New Guinea and parts of eastern Australia. They
are famous for the elaborate courting displays, plumage ornaments and dramatic
colouration of the males. In many species, males have brightly coloured patches
of feathers next to matte black plumage that appears much darker than the black
colouration of other birds. When researchers from Harvard University, the
Smithsonian Institution, and Yale University shone light on museum specimens of
five species of the bird of paradise they discovered that these black feathers
have an extremely low directional reflectance – at normal incidence they only
reflect back 0.05–0.31% of light. In contrast, black feathers from two other
species of bird, used for comparison, had a directional reflectance of
3.2–4.7%. . . . .
(Experiments). . . done by the team revealed that this is a result of the
feathers' microscopic structure. A typical feather has a central shaft with
rows of barbs branching off. Rows of smaller barbules then spread out from the
barbs. In most feathers this structure is flat, with everything laying in the
same horizontal plane. But the super-black feathers have barbules that are
covered in microscale (tiny) spikes and they curve away (up) from the
horizontal plane. The researchers explain that these vertically-tilted barbule
arrays create deep, curved cavities that cause multiple scattering of light,
resulting in more structural absorption of light than normal black feathers. ".
. . . These super-black feathers even retained their black appearance when
coated with gold dust, whereas the normal black feathers appeared gold”.
The modified barbules are only present on the exposed overlapping tips of the
feathers, while those towards the base of the feathers have a typical feather
structure. Also, the black feathers from the back of one bird of paradise
species, the superb bird-of-paradise, Lophorina superba, which are not used
during display, had a typical barbule morphology and were more reflective than
the super-black feathers. This supports the idea that the modified feathers
have evolved for display purposes, the researchers say.
Nari B. Mistry,
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