Going gray is something most people worry about at some point in their lives. Curiously, birds do not share the same problem, as their plumage always remains a vibrant collage of colors until they die. Scientists have now discovered how this is possible, at least in terms of the Eurasian Jay: It generates its patterns by manipulating the growth of many tiny structures on its feathers, instead of using dyes or pigments that would fade over time. The new findings are published today in the journal Scientific Reports.
Jays are several species of noisy, colorful birds belonging to the crow family, Corvidae. Their vivid colors are thought to be used for both attracting a mate and for simply telling each other apart, but it has not been known before how they are able to produce such beautiful, colorful plumage. In order to investigate this mystery, a team of researchers from the University of Sheffield took some blue and white Jay feathers to the European Synchrotron Radiation Facility (ESRF) in France.
The Jay’s feather, which is able to go from ultraviolet and blue to white in hue, is constructed out of a protein complex called keratin, the same material human hair and fingernails are made from. At the nanoscale, this keratin appears to be somewhat “spongy,” in that it contains a plethora of minuscule holes.
Image credit: The “spongy” keratin nanostructures. Parnell et al./Scientific Reports
These nanoscale-sized holes were viewed at the ESRF using a technique called X-ray scattering, a non-destructive process that looks at how X-rays bounce off incredibly small structures. The researchers found that these holes can be fixed to any chosen size as the keratin-based feathers grow and develop, determining the colors we see. Light hitting the feathers will be scattered differently depending on the sizes of the holes, meaning that any light that reflects back and reaches our eyes will appear to be a different color depending on the sizes of the holes it scattered through.
The same principle operates in our own atmosphere. The reason the sky is blue is because that wavelength of light scatters more frequently than others off suspended particles. Similarly, holes of a certain size on the feathers of a Jay will scatter the blue wavelengths of light more frequently, making them appear to be blue to the observer. If the holes shrink and thus scatter shorter wavelengths, they may appear to be purpler.
Different parts of the feathers can hold different hole sizes, meaning that multiple colors can exist along one single feather. Although this was only observed on Jays, the researchers believe that it is this ability to order nanostructures that means that any bird’s colorful plumage never fades over time.
Intriguingly, the color green is still difficult to produce, even with this remarkable ability to manipulate the sizes of these tiny holes. In order to generate a viridian color, a yellow pigment is required to absorb some of the scattered blue light.
Much of our own society relies on using pigments and dyes to produce color, but this type of nanoscale manipulation demonstrates how vibrant, unfading colors could be used instead. “If nature can assemble this material 'on the wing', then we should be able to do it synthetically too,” said Andrew Parnell, the lead author of the study, in a statement.