When mallards storm off, they really storm off, giving everyone a good look at their bright blue backsides as they swim away. Scientists have long struggled to explain how ducks like these (shown) produce such brilliant blues, greens, and bronzes, usually squeezed into patches on their wings. So researchers decided to take a closer look at duck plumage, observing feather filaments belonging to four species, including the mallard (Anas platyrhynchos), under an electron microscope. These curious birds, it turns out, owe their hues to their inner hexagons, the team reports online today in the Journal of the Royal Society Interface. Each of the ducks has a thin layer composed of hundreds of pigment-bearing structures—or melanosomes—lining the interiors of their feathers (inset). Light hitting these solid shapes, which stretch about 60 to 85 nanometers across, bounces away, producing highly saturated colors. But ducks, unlike other birds with similar structures, have six-sided, not square-shaped, melanosomes. These hexagons are versatile, too: With slight tweaks to the pattern, different duck species have been able to reflect visible light spanning most of the rainbow. So in any palette, the birds get their flashy exits.
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