A new study published in the journal Royal Society Open Science revealed a surprising discovery: 37 out of 45 known species of birds-of-paradise exhibit biofluorescence, emitting green or yellow-green light when exposed to blue or ultraviolet (UV) light.
Researchers from the American Museum of Natural History and the University of Nebraska-Lincoln conducted an analysis of birds-of-paradise specimens preserved since the 19th century, including the Emperor Bird of Paradise (Paradisaea guilielmi). According to GEO France, the team discovered that biofluorescence—previously a little-explored trait in avian species—is present in many of these birds.
Biofluorescence is a phenomenon where an organism absorbs light at one wavelength and re-emits it at a different, longer wavelength, producing a light effect that is hidden from the human eye. This effect may make birds-of-paradise brighter and more eye-catching to each other, enhancing visual communication during courtship.
"In males, biofluorescence occurs on the bright plumage and skin that are highlighted and used during courtship displays, hierarchy among individuals, or before copulation with a female," states the study.
Male birds-of-paradise are renowned for their vivid plumage and elaborate mating dances, including wing beats, fluttering, and fascinating poses. They often choose courtship arenas that enhance the visibility of their colorful feathers. Biofluorescence has been observed in areas related to mating displays, such as the beak, head, neck, and belly, which are prominent during courtship and may play a crucial role in attracting mates and establishing dominance.
"It seems fitting that these flashy birds are likely signaling to each other in additional, flashy ways," said Rene Martin, the lead author of the study.
The researchers found that biofluorescence is most pronounced in male birds, particularly in feathers and skin areas prominent during courtship displays. In contrast, female birds-of-paradise showed biofluorescence mainly in the chest and abdomen, with patterns that are much more subtle compared to males and much less common overall.
Birds-of-paradise inhabit the dense tropical forests of New Guinea, Indonesia, Papua New Guinea, and eastern Australia, where sunlight filters complexly through the foliage, providing high light levels throughout the year.
Biofluorescence is known from many animals, including species of fish, amphibians, and mammals such as bats, wombats, sugar gliders, and platypuses, as well as in some species of birds. In recent years, scientists have found biofluorescence in fish, salamanders, sea turtles, and species of mammals and marsupials.
"Despite there being over 10,000 described species of birds and numerous studies on their coloration and vision, surprisingly few have investigated biofluorescence in them," John Sparks, curator at the American Museum of Natural History, stated.
The team discovered that birds-of-paradise have eye pigments that match the peaks of fluorescence detected.
Emily Carr, a PhD candidate at the Richard Gilder Graduate School, explained that the environment of birds-of-paradise, including abundant sunlight and varying canopy density, could amplify the biofluorescence phenomenon, enhancing communication and recognition among individuals.
The article was written with the assistance of a news analysis system.