No abstract

We conducted two-dimensional (2D) discrete Fourier analyses of the spatial variation in refractive index of the spongy medullary keratin from four di¡erent colours of structurally coloured feather barbs from three species of bird: the rose-faced lovebird, Agapornis roseicollis (Psittacidae), the budgerigar, Melopsittacus undulatus (Psittacidae), and the Gouldian ¢nch, Poephila guttata (Estrildidae). These results indicate that the spongy medullary keratin is a nanostructured tissue that functions as an array of coherent scatterers. The nanostructure of the medullary keratin is nearly uniform in all directions. The largest Fourier components of spatial variation in refractive index in the tissue are of the appropriate size to produce the observed colours by constructive interference alone. The peaks of the predicted re£ectance spectra calculated from the 2D Fourier power spectra are congruent with the re£ectance spectra measured by using microspectrophotometry. The alternative physical models for the production of these colours, the Rayleigh and Mie theories, hypothesize that medullary keratin is an incoherent array and that scattered waves are independent in phase. This assumption is falsi¢ed by the ring-like Fourier power spectra of these feathers, and the spacing of the scattering air vacuoles in the medullary keratin. Structural colours of avian feather barbs are produced by constructive interference of coherently scattered light waves from the optically heterogeneous matrix of keratin and air in the spongy medullary layer.

Plumage is a complex component of the avian phenotype. The plumage of an individual is composed of numerous hierarchically arranged developmental and morphological modules. We present a hierarchical model of plumage that provides an intellectual framework for understanding the development and evolution of feathers. Independence, covariation, and interaction among plumage modules create numerous opportunities for developmental and evolutionary diversification of feather complexity and function. The hierarchical relationships among plumage modules are characterized by both top-down and bottom-up effects in which properties of modules at one level of the hierarchy determine or influence the properties of modules at lower or higher levels of the hierarchy. Plumage metamodules are created by covariation or interaction among modules at different levels of the hierarchy.

No abstract

Measurements have been made of the spectral reflectance of the dorsal skin of living tree frogs, Hyla cinerea.The colors assumed by the frogs when placed on backgrounds of different colors varied with respect to both dominant wavelength (565-580 nm), purity (42-58%) and lightness (2-19%).