Structural and Compositional Analysis of Feathers of Sunbird Nectarinia Asiatica

Abstract

The plumage of many birds is highly attractive, especially when thefeathers are patterned in strongly contrasting colours. Orange colours are generally caused by pigments that selectively absorb short-wavelength light. When these pigments are embedded in a diffusive medium, only the long-wavelength part of incident broadband light is reflected and scattered. In contrast, blue or green animal coloration is virtually always due to periodic structures that reflect and scatter incident light of a restricted short-wavelength range(Srinivasarao, 1999; Vukusic and Sambles, 2003; Kinoshita and Yoshioka, 2005; Prum, 2006). Pigmentary and structural coloration are often found simultaneously, not only in birds but also in many other animals, for example butterflies, beetles and lizards (Kinoshita,2008). Birds possess various pigment classes, for instance carotenoids, pterins, porphyrins, psittacofulvins and melanins (McGraw, 2006; Hill and McGraw, 2006), and various mechanisms of structural colouration, namely thin films, multilayers, photonic crystals, keratin spongy nanostructures and nanofibres (e.g. Durrer, 1977; Shawkey et al., 2003;Shawkey et al., 2006; Yoshioka et al., 2007; Doucet and Meadows, 2009; Prum et al., 2009; Stavenga et al., 2010; D’Alba et al., 2011). The predominant location of colouration is the feathers, often either the barbs or the barbules. Structural coloration of avian skin have been long hypothesized to be produced by incoherent(Rayleigh /Tyndall )scattering. Avian plumage color have emerged recently as model system for investigating the type of information that can be signaled by showy sexual display in birds.The non pigmentary colors of the tissues of living organism are produced by physical interaction of light with nanostructures in the tissues. The brilliant iridescent color appearances of many avian feathers are produced by complex optical phenomena. They principally arise from coherent light scattering from self-assembled quasi-ordered structures that have a spatially periodic variation in refractive index. Iridescent structural colors in biology exhibit sophisticated spatially-varying reflectance properties that depend on both the illumination and viewing angles. The classification of such spectral and spatial information in iridescent structurally colored surfaces is important to elucidate the functional role of irregularity and to improve understanding of color pattern formation at different length scales