Of the more than 9,000 species of birds found around the world, there is only a small handful of species that are predominantly blue in color. Not only is it relatively rare to be blue, but how the color is created may come as a bit of a surprise. Some colorful birds get their color based on their food. For instance, flamingoes are pink because they get their pigment from the shrimp and algae they eat. But birds sporting blue feathers, do not rely on pigment for their unique color. So how does it happen?
Richard Prum, an ornithologist at Yale, decided to look into the matter. He and his team analyzed thousands of feathers and discovered the secret to how blue feathers get their color.
Smithsonian writes, "Prum discovered that as a blue feather grows, something amazing happens. Inside each cell, stringy keratin molecules separate from water, like oil from vinegar. When the cell dies, the water dries away and is replaced by air, leaving a structure of keratin protein interspersed with air pockets, like a sponge or a box of spaghetti. When white light strikes a blue feather, the keratin pattern causes red and yellow wavelengths to cancel each other out, while blue wavelengths of light reinforce and amplify one another and reflect back to the beholder’s eye. The result: blue, an example of what scientists call a structural color (as opposed to a pigmented color) because it’s generated by light interacting with a feather’s 3-D arrangement. And different shapes and sizes of these air pockets and keratin make different shades of blue."
Want to test this out for yourself? Cornell Lab of Ornithology tells us how: "If you find the feather of a Blue Jay or Steller's Jay you can see for yourself how this works. First, observe the feather in normal lighting conditions and you will see the expected blue color. Next, try back-lighting the feather. When light is transmitted through the feather it will look brown. The blues are lost because the light is no longer being reflected back and the brown shows up because of the melanin in the feathers."