Structural color -- that's engineer speak for a reflective display that mimics iridescence.

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They are flashes of iridescence, their wings beating so fast they are virtually invisible, their beaks as thin as needles.

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Intriguingly, that did not apply to birds that used melanin, another pigment, in their plumage, nor to those that employed iridescence which is a result of the structure of feathers, rather than their chemistry.

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