Structural Color in the Little Blue Penguin

How do birds get their color?  Light absorption  by pigments is one way color can be produced.  Bird feathers have pigments like melanins and carotenoids – we even have evidence for color in the fossil penguin Inkayacu from fossilized melanin-bearing structures.  Color can also be produced by physical interactions between light and biological nanostructures. These colors are called structural colors.

Left: Microscope image of keratin nanofibers in a penguin feather (photo by Liliana D’Alba). Right: Little Blue Penguin, taking a break at the aquarium.

Recently the color of Little Blue Penguins was found to be generated by a new type of structural color.  As their name implies, Little Blues are both small and wrapped in bluish feathers.  A previously unrecognized nanostructure is responsible for the blue feather barbs of these penguins.   Structural color can be generated by several different types of structures, such as tiny spheres or channels.  However, researchers were surprised to find a completely unknown nanostructural arrangement in the penguin feathers.  At the subcellular level, Little Blue Penguin feather barbs are composed of parallel b-keratin nanofibres organized into densely packed bundles.  Essentially, the miniscule structures  scatter light waves so as to give off blue color.

This is an important discovery, because learning how birds make color at the nanostructural level may help scientists synthesize artificial colored structures in the lab.  Of course, it also has implications for penguin evolution.  We are only beginning to understand how the microstructure of feathers affects their function in the air and under water.  Exciting research is on the horizon, and future investigations may yield a better understanding of what exactly makes  penguin feathers so efficient at insulation and streamlining.

Reference:

D’Alba L; Sarananthan V; Clarke JA; Vinther JA; Prum RO; Shawkey MD. 2011. Colour-producing β-keratin nanofibres in blue penguin (Eudyptula minor) feathers. Biology Letters. February 9 doi: 10.1098/rsbl.2010.1163: 1