Feathers are inherently what makes a bird a bird, yet their nature and origin have long mystified some of history’s brightest minds, from Aristotle to Newton. Today’s scientists are trying to better understand how and why jays glow so blue, parrots so green, flamingoes so pink. Using such high-tech tools as electron microscopy and high-speed video, they’ve been learning that feathers are multitaskers, carrying out multiple jobs simultaneously. They’re flight surface, rain jacket, and courting outfit. They’re a barometer of what a bird has been eating and how it has been living. In some cases they comprise a potent preventive medicine. Much of what we’ve always loved about this delicate medium through which birds meet the world is precisely what meets the eye—yet much of what we can learn to appreciate about them, it turns out, lies just a little beyond our normal range of vision. ANATOMY #1A feather develops much like one of our hairs—a meticulously constructed mass...