This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The brilliant magenta feathers on the head and throat of a male Anna's hummingbird present an optical puzzle. Magenta cannot be produced by a single wavelength of light.
Instead, the feathers reflect a mixture of red and blue. Scientists understood the strong red reflection, but the weaker blue component was harder to explain. Sangyeop Kim of Yonsei University and colleagues have now identified a previously overlooked region inside the feathers that helps supply the blue reflection.
Their study in the Journal of the Royal Society Interface shows that this buried region works together with material near the surface to produce the distinctive color. The team tested their explanation by gradually eroding the surface of the feather. As the blue reflection faded, the feathers' appearance changed from magenta to orange.
Scientists already knew that these feathers owe their shimmering appearance to their internal architecture. A 2018 study measured the strong red and weaker blue reflections and modeled how stacked structures inside the feathers produced them. The calculations explained much of the color, but did not fully reproduce the blue component.
The new work examined those stacks more closely. They sit inside barbules, the tiny branches extending from a feather's larger branches. Each stack contains flattened structures called melanosomes, which hold the pigment melanin.
In Anna's hummingbird, these structures also contain air cavities and are embedded in feather protein. Light waves reflected from the boundaries between these materials overlap, strengthening some colors and weakening others. The thickness and arrangement of the layers therefore help determine the color we see.
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