#funfactfriday Happy Hanukkah! Hanukkah Sameach!
The traditional colours of Hanukkah are blue and white, which makes the Mountain Bluebird particularly festive!
But did you know that bluebirds aren't actually blue?? In comparison to red or yellow birds, who get their colour from pigment molecules in their feathers, all blue-coloured birds get their colour from prism-like light reflection in their feathers. The physical structure of a bluebirds feather has stringy bits of keratin protein woven in it with air pockets in between. As light hits the feathers, this keratin structure absorbs most light, but reflects blue light back to our eye so all we see is beautiful blue!
There are many other examples of "structural colour" in nature, including butterfly wings, some fish scales, and even a few brilliantly coloured berries and flowers! The colour-changing abilities of chamaeleons and cephalopods like octopi are extreme examples of structural colour.