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.
========================= 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