Abstract

The source of the blue color of blue jay feathers has been attributed to scattering since the mid-nineteenth century after it was found that no pigments could be extracted from the feathers. The transmittance and scattering properties of blue jay feathers were measured as a function of wavelength between 0.36 and 0.74 μm. The transmittance in the red region of the spectrum was found to be considerably higher than the transmittance in the blue region. The peak transmittance occurs at a wavelength of 0.63 μm. Scattering measurements revealed an intensity maximum at shorter wavelengths and a minimum at longer wavelengths. A computer analysis of the scattered intensity yielded an exponential dependence on wavelength. The exponent ranged from −3.98 to −4.44 for diffuse scattering geometries and −2.67 for the specular scattering geometries compared with the value of −4.0 expected for Rayleigh scattering. The feathers used in this experiment were rectrices. The barbs have a transparent outer layer underlain by a layer of box cells or alveolar cells, beneath which there is a dark layer of melanin-containing cells. The alveolar cells contain irregularly shaped air cavities ranging in size from 0.03 to 0.3 μm. The air cavities are responsible for the scattering dependence.

© 1986 Optical Society of America