Structural Coloration in Caloenas Nicobarica Pigeons and Refractive Index Modulated Sensing

Abstract

The Nicobar pigeon (Caloenas Nicobarica) belongs to the extinct dodo‐bird family and has been declared as an endangered species. Here, microscopic and spectroscopic measurements are carried out on the bird's feathers to study the structural coloration originating from the barbule nanostructures. A range of color shades is recorded with changing viewing and illumination angles at different locations of the feathers. A spectacular variation in colors is generated by photonic structures; red, green, and blue and their blends are observed. Hydrophobicity of the optical material is also investigated. A contact angle of ≈156° is observed demonstrating it to be superhydrophobic. Experimental observations of the optical properties are analyzed on these feathers for sensing made possible due to the material and structural properties at the interface between barbule's surface and solution. An optical response is observed with a redshift in optical spectra with increasing refractive index of the solution, which is correlated with concentration values. The structural coloration in Nicobar pigeon can be adopted for many practical applications such as color selective filters, nonreflecting coatings, and refractive index‐based sensing.

Bioinspired Superhydrophobic Thermochromic Films with Robust Healability

“…In nature, some bird species, such as Nicobar pigeon, Anna hummingbird, and dabbling duck, etc., have beautiful iridescent feathers with color-shifting capability. When changing illuminations or viewing angles, their feather exhibits vivid color changes due to the special photonic structure.…”

“…When changing illuminations or viewing angles, their feather exhibits vivid color changes due to the special photonic structure. To maintain such a unique color-changing feature (as well as for some other reasons such as surviving from aqueous living environments), the iridescent feather of such birds also typically exhibits superhydrophobicity, which endows the feather with self-cleaning capability to remove small-scale dusts that may destroy the photonic structure to deteriorate the iridescence. , For example, Nicobar pigeon’s feather demonstrates superhydrophobicity with a high water contact angle (CA) of 156° due to the orderly arranged micro- and nanoscale surface texturing . On the other end, mechanical damage is another main cause for the deterioration/loss of chromism, especially during real-life applications.…”

Biological Material Interfaces as Inspiration for Mechanical and Optical Material Designs

“…Naturally occurring iridescent systems endow the creatures with spectacular visual displays through the coupling effects of interference, diffraction, absorption, and scattering. Well-studied biological iridescent systems include shimmering scales of butterfly wings, flashing elytra of beetles, sparkling feathers of birds, , twinkling skins of cephalopods, glittering cuticles of fruits, brilliant petals of flowers, and colorful surfaces of opals (Figure A) . These natural iridescence systems play essential roles in signaling, camouflage, sexual selection, and enhancing vision, due to the striking appearance and unique optical properties. − …”

Chemical Fabrication Strategies for Achieving Bioinspired Superhydrophobic Surfaces with Micro and Nanostructures: A Review

“…[ 46 ] The feathers of Nicobar pigeon are made up of well‐ordered micro/nano surface textures, exhibiting excellent water repellency with a high WCA of 156° and structural coloration. [ 47 ] These plants and animals with unique properties provide guidance for the design of artificial superhydrophobic surfaces.…”