Birds-of-paradise have long fascinated scientists with their dazzling courtship displays, but new research reveals they have an even more striking secret—they glow under ultraviolet light!
Scientists have discovered widespread biofluorescence in these birds, with males showcasing neon hues on their bills, feet, and feathers, likely to impress mates and establish dominance. This revelation suggests that their already extravagant displays may be even more complex than we imagined, with “hidden” signals only visible to their own kind.
Birds-of-Paradise Glow in a New Light
Scientists from the American Museum of Natural History and the University of Nebraska-Lincoln have made a groundbreaking discovery: birds-of-paradise exhibit widespread biofluorescence. This is the first time researchers have documented this glowing phenomenon across the species, with 37 out of 45 known birds-of-paradise displaying biofluorescence. The study, which analyzed specimens collected since the 1800s, suggests that this glow plays a key role in male birds’ social hierarchy and mating displays. The findings were published recently in Royal Society Open Science.
“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 the study’s lead author Rene Martin, an assistant professor at the University of Nebraska-Lincoln who conducted this work when she was a postdoctoral researcher at the Museum. “It seems fitting that these flashy birds are likely signaling to each other in additional, flashy ways.”
What Is Biofluorescence?
Biofluorescence occurs when an organism absorbs light and re-emits it as a different color. Museum Curator John Sparks, an ichthyologist, has studied biofluorescence in a wide range of species, particularly in fish. His research team has used specialized photography techniques — combining ultraviolet and blue lights with emission filters — to document biofluorescence in animals including sharks, turtles, and corals. About a decade ago, Sparks collaborated with Museum ornithologists to investigate whether birds with complex courtship behaviors also fluoresce. This latest study builds on that early work, confirming that birds-of-paradise do, in fact, glow in ways previously unknown.
“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.
The Birds That Glow in the Dark
Bowerbirds and fairy wrens failed to glow, but among birds-of-paradise, Sparks found bright green-yellow fluorescence. Sparks’ initial work was continued recently by Martin and Emily Carr, a Ph.D. student in the Museum’s Richard Gilder Graduate School. Together, the team took a closer look at biofluorescence in birds-of-paradise, which live across eastern Australia, Indonesia, and New Guinea, finding that the birds also fluoresce when exposed to UV light, not just blue light. This phenomenon is especially prominent in males, focused on their bright plumage and skin in areas that are highlighted during displays: the inner mouth and bill, feet, and feathers on the head, neck, and belly. In females, biofluorescence is usually restricted to plumage on the chest and belly.
“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.
A Hidden Signal in the Eyes of Birds
Studies based on closely related species found that the pigments in the birds’ eyes align with the fluorescence peaks that the researchers measured. Based on this, the authors infer that birds-of-paradise can see these biofluorescent patterns, which enhance contrast against dark plumage and possibly play an important role in courtship and hierarchy.
Reference: “Does biofluorescence enhance visual signals in birds-of-paradise?” by Rene P. Martin, Emily M. Carr and John S. Sparks, 1 February 2025, Royal Society Open Science.
DOI: 10.1098/rsos.241905
Funding for this work was provided by the American Museum of Natural History’s Department of Ichthyology, the Richard Gilder Graduate School, and the Gerstner Scholarship.
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