Date: 2/1/18 8:03 am
From: Nari Mistry <nbm2...>
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.

Nari Mistry

========================= 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*,
Ithaca, NY
To see my paintings, visit
http://www.ArtbyNari.com

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