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Whether they’re whipping their heads dramatically, contorting into seemingly impossible shapes, or trapping light in their plumage like a black hole, birds-of-paradise always seem to have a new trick up their feathers. The family of flamboyant species, found only in the dense rainforests of Australasia, have earned plenty of attention for their flashy looks and moves over the years. But new research reveals these birds have another dazzling feature that’s been hiding in plain sight.

Most birds-of-paradise are biofluorescent, meaning they absorb light from the sun and then emit it as a different color, according to a new study published in the journal . Their vivid patches don’t just look bright—they really gleam, transforming ultraviolet rays into their own colorful glow for other birds to see. After analyzing birds-of-paradise specimens stored in the American Museum of Natural History’s collections, researchers found the trait in 37 out of 45 known species.

A team of ichthyologists, who previously found biofluorescence is , made the discovery after becoming interested in finding out what other creatures in the museum’s collections had this novel ability. Based on where they found the fluorescent feathers and what scientists currently know about these birds, the research team believes these showy feathers enhance mating rituals and help determine social hierarchies for birds-of-paradise.

Even though the birds already have an abundance of fabulous plumage, “it could just be that the biofluorescent portions are helping enhance those displays even more,” says lead study author Rene Martin, a fish biologist at the University of Nebraska-Lincoln.

For human observers, these glowing patches aren’t visible to the naked eye. But for birds, which have an extra type of photoreceptor, or cone, in their eyes that helps them see more colors and UV light, the fluorescence could help their mating displays pop, explains study co-author Emily Carr, a PhD student at the American Museum of Natural History. They also have oil droplets in their eyes that help them to filter light and see fluorescent wavelengths easier than we can, Carr says.

To mimic that extra-colorful vision, the study authors analyzed the museum’s specimens—many of which are more than 100 years old— by shining a UV light that “excites” the molecules that cause fluorescence. Then, they viewed the birds through yellow goggles that filter the light and make the fluorescent areas shine. In 82 percent of the species they viewed, the result was a burst of yellowish-green. “You’ll open a drawer, and you’re not quite sure what to expect,” Martin says. “You finally hit a new genus or a new species, and they’ll just have these huge patches of extremely bright feathers that your light is just gleaming off of.”

To see the biofluorescence is a “very psychedelic” experience, adds John Sparks, co-author of the study and a curator at the American Museum of Natural History. Usually, fluorescence gets “swamped out” by the ambient light around us, he says, “but all that light—that fluorescence—is there.”

Scientists have now discovered biofluorescence in a growing range of birds—along with other creatures from geckos to platypuses—and they’ve been working to better understand how species use this special power in their daily lives. In 2016, one team found that the beaks of Atlantic Puffins similarly glow, possibly to also attract mates. 

Among the 37 biofluorescent birds-of-paradise, almost all species had fluorescent patches inside their mouths, which many of the male birds show off during mating rituals. But the locations of other glowing feathers varied by species: Some had fluorescent feathers on their long tails, while others had patches on their breasts and bellies or around their eyes.

“To me, the interesting part is that it's so widespread throughout the group,” says Edwin Scholes, who founded the at Cornell Laboratory of Ornithology and was not involved in the study. “It's not just all tail feathers or all flank feathers or anything specific—it's pretty much all over the board.”

Researchers found that the eight bird-of-paradise species without biofluorescence—all from the genera Lycocorax, Manucodia, or Phonygammus—are more “monogamous” birds that have less competition finding mates than their glowing peers. Out of the species that did give off light, both male and female birds-of-paradise had biofluorescent plumage. But the females had dimmer and more “mottled” fluorescent feathers, Carr says, further supporting the idea that males use the feathers for mating rituals.

How exactly birds-of-paradise can take advantage of this newly discovered trait in the shadowy forests they call home remains an open question. Bright light may help these bird’s fluorescent patches to gleam, the study suggests—but in the dense rainforests of Australasia, sunlight is patchy and inconsistent. And the birds tend to prefer to perform their courtship displays on overcast days, according to Scholes, who has studied these birds in their native habitat for many years. 

He hopes firsthand observations of these birds will help illuminate the purpose behind their biofluorescence and how visible it is in the wild. “I say it's a field that's wide open,” Sparks adds. “The ornithologists really need to get out there and study this.”