New research has revealed that biofluorescence is widespread in birds-of-paradise, a group of tropical birds famous for their spectacular courtship dances and colorful plumage.
The study shows that 37 out of the 45 known species exhibit biofluorescence, which appears to be especially prominent in males. This hidden glow may be used to attract mates and establish dominance.
The research was conducted by scientists at the American Museum of Natural History (AMNH) and the University of Nebraska-Lincoln.
Adding a glow to mating rituals
Birds-of-paradise inhabit regions in eastern Australia, Indonesia, and New Guinea. For generations, they have intrigued scientists with elaborate feather displays and acrobatic dances that males use to court females.
Bioluminescence is a phenomenon in which an organism absorbs light at one wavelength, then emits it at another
The new evidence of biofluorescence suggests that these dazzling birds might have yet another visual trick: a layer of fluorescent signals invisible to humans without specialized instruments.
Rene Martin is the study’s lead author and an assistant professor at the University of Nebraska-Lincoln.
“The unique mating rituals and displays of birds-of-paradise have fascinated scientists and spurred a myriad of studies focused on trait evolution and sexual selection,” said Martin. “It seems fitting that these flashy birds are likely signaling to each other in additional, flashy ways.”
Detecting fluorescence in birds-of-paradise
The research draws on specimens collected since the 1800s, held in the American Museum of Natural History’s extensive ornithology collection.
A decade ago, Museum Curator John Sparks – an ichthyologist by training – noticed that certain bird species, including some birds-of-paradise, glowed green-yellow when exposed to specific wavelengths of light. This led him and colleagues to begin a deeper exploration of avian biofluorescence.
“Despite there being over 10,000 described avian species, with numerous studies that have documented their bright plumage, elaborate mating displays, and excellent vision, surprisingly very few have investigated the presence of biofluorescence,” Sparks said.
Martin, who conducted this work while a postdoctoral researcher at the Museum, and Emily Carr, a PhD candidate in the Museum’s Richard Gilder Graduate School, took Sparks’ initial findings and broadened the analysis.
Using ultraviolet (UV) light, the team discovered that the birds not only glow under blue wavelengths but also fluoresce strongly under UV exposure.
This effect was mainly observed on male plumage patches crucial to courtship, such as the head, belly, and neck, as well as mouth and bill linings.
Biofluorescence is most pronounced in males
The researchers found that this fluorescence is especially vibrant in males, often concentrated in areas highlighted during mating rituals.
Meanwhile, females also exhibit it, though to a lesser degree – primarily on their chests and bellies. The study suggests that the equatorial environments in which these birds live offer abundant and varied light conditions, possibly enhancing the visibility and function of biofluorescence.
“These birds live near the equator, where there is an abundance of bright solar light year-round, and they live in forests where the complexity of light is significantly affected by differences in the canopy and where biofluorescent signals may be enhanced,” Carr said.
Why bird fluorescence matters
Recent studies in closely related species indicate that birds-of-paradise have eye pigments aligned with the fluorescence peaks measured in this study – meaning they can likely perceive these glowing patches.
In a species group already known for visually striking performances, these fluorescent signals may offer an even finer scale of detail for courtship and territorial displays.
When a male bird-of-paradise performs an intricate dance, the green-yellow glow from certain feathers might act like a hidden spotlight, contrasting sharply against the bird’s darker plumage. This could help catch a female’s attention or signal social status among competitors.
Implications for avian research
Although birds-of-paradise are among the best-studied avian groups for behavior and coloration, the discovery of broad-scale fluorescence suggests that birds may have more complex signaling systems than previously realized.
The presence of fluorescent patches in so many species raises the possibility that other bird lineages, especially those with striking plumage or elaborate displays, could also exhibit biofluorescence.
Moving forward, the researchers plan to investigate how environmental factors – like canopy cover, seasonal light availability, and even habitat degradation – might affect these glowing displays.
Understanding how birds-of-paradise perceive biofluorescence could also inform broader questions about the evolution of sexual selection and signaling in avian species.
Ultimately, this study reshapes scientists’ understanding of the “secret language of light” that these flamboyant birds use to communicate.
With improved imaging technologies and heightened awareness of avian fluorescence, researchers may soon discover that a hidden glow permeates many corners of the bird world, especially in those known for their spectacular visual allure.
The study is published in the journal Royal Society Open Science.
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