UC Botanical Garden, Berkeley, California. Credits: Watershed Project / Creative Commons.A male Anna’s hummingbird can flash an almost electric magenta, so vivid it looks artificial. But there’s nothing artificial about it. And there’s no magenta pigment responsible for the display.
Instead, the bird uses microscopic structures inside its feathers to manipulate sunlight, reflecting red and blue light together to produce a color that no single wavelength can create.
Now, scientists have discovered an overlooked layer inside those feathers that helps make this extraordinary optical trick possible.
A color that doesn’t exist in the rainbow
Male Anna’s hummingbirds display brilliant magenta feathers across their heads and throats.
Think of a rainbow. It contains red, orange, yellow, green, blue and violet, along with the colors between them. Each corresponds to a particular range of wavelengths of visible light.
There’s no magenta in the rainbow.
That’s because there’s no single wavelength of magenta light. Unlike violet, which appears at the short-wavelength end of the visible spectrum, magenta emerges when our visual system processes a combination of red and blue light. It’s what scientists call a non-spectral color.
And Anna’s hummingbirds (Calypte anna) have evolved a particularly elaborate way to produce it.
These birds, common along the Pacific Coast of North America, have brilliant reddish-pink feathers covering their crowns and throats. But turn a male’s head just slightly, and that dazzling magenta can suddenly become dark, almost black, before flashing back into view.
This phenomenon is called iridescence. It happens because extremely small structures selectively reflect different wavelengths of light, much like the shimmering colors of soap bubbles or oil slicks.
Hummingbirds aren’t the only birds to have iridescent feathers. Peacocks and starlings are familiar examples. The broad principles behind iridescence are also well understood. What remained mysterious was how Anna’s hummingbirds managed to reflect two separate parts of the visible spectrum simultaneously, producing such an intense magenta.
Peacocks are another species of birds that creates colors without pigments. Image via Wiki Commons.A tiny optical machine
To get to the bottom of the mystery, researchers measured light reflected by the birds’ throat feathers. They found a dominant peak at approximately 632 nanometers — firmly in the red part of the spectrum. That means the feathers reflect particularly strongly at this wavelength, which our eyes perceive as red light.
Together, these two peaks produce the bright magenta. The red peak was nearly three times as strong as the blue one, giving the resulting color its distinctive reddish-pink appearance.
But where was that blue light coming from?
To find the missing piece, researchers from Yonsei University in South Korea and Ghent University in Belgium examined the feathers using electron microscopy and three-dimensional imaging.
They focused on the barbules, the tiny branches extending from individual feather barbs. Inside each barbule, they found an intricate arrangement of flattened structures called melanosomes. These are organelles that contain melanin, the pigment responsible for many dark colors in animals.
But hummingbird melanosomes are unusual. They’re flattened into tiny platelets containing air-filled cavities, and they’re arranged in overlapping layers within a protein matrix.
Each boundary between air, melanin and protein changes how light travels through the feather. When light reflects from the different layers, some wavelengths reinforce one another while others interfere destructively.
The result is a highly selective natural reflector.
And its secret lies in a microscopic layer that researchers had previously overlooked.
Image via Wiki Commons.Earlier research had generally divided these structures into two size categories: small melanosomes near the surface and larger ones underneath.
But the researchers found another, intermediate size category, consisting of two layers sandwiched between the surface structures and the larger, deeper melanosomes.
The dimensions were extraordinarily precise. The smaller, surface melanosomes averaged just 108 nanometers thick. The intermediate ones measured approximately 189 nanometers, while the larger, deeper structures averaged 222 nanometers. For perspective, a human hair is tens of thousands of nanometers wide.
Neither the surface layer nor the intermediate layer could produce the distinct blue peak on its own. Researchers used computer simulations to show that the optical effect emerged from their interaction.
They also conducted real-life experiments. They used oxygen plasma to gradually strip away the top layer. After 60 seconds of treatment, the original magenta began shifting toward reddish-orange. After 120 seconds, the feathers appeared yellowish-orange.
Measurements revealed what had happened: the blue reflectance peak weakened and eventually disappeared, while the dominant red peak shifted toward shorter wavelengths.
What do birds see?
There’s another twist to this story. Birds don’t see the world nearly the same way we do.
Humans have three types of color-sensitive cone cells in their eyes. Birds typically have four, including one sensitive to ultraviolet light.
Basically, birds (including hummingbirds) see combinations of colors that humans can’t directly experience. In a 2020 study published in PNAS, researchers demonstrated that wild hummingbirds could distinguish several non-spectral color combinations, including ultraviolet-plus-green and ultraviolet-plus-red.
This raises an intriguing question: what does the dazzling magenta of Anna’s hummingbird actually look like to another hummingbird? We can’t know exactly from the human-visible reflection alone.
Male Anna’s hummingbirds use their iridescent throat feathers during elaborate courtship displays. They even orient their aerial dives relative to the Sun so that their brilliant plumage flashes toward a potential mate.
The new research doesn’t establish that the particular arrangement of melanosomes evolved specifically for mating success. But it reveals just how sophisticated the physical machinery behind these visual signals can be.
The implications may also extend beyond birds.
Engineers are increasingly interested in structural colors because carefully designed nanostructures can produce intense colors without relying on conventional dyes. Understanding how hummingbirds combine different reflection peaks could inspire new optical coatings and materials capable of producing complex colors.
For now, however, nature has a considerable head start.
Journal Reference: Sangyeop Kim et al., Multi-periodic photonic mechanism for non-spectral magenta coloration in Anna’s hummingbird (Calypte anna) feathers, Journal of the Royal Society Interface (2026). DOI: 10.1098/rsif.2026.0601
