Birds-of-Paradise Found to Be Biofluorescent

In the past decade, Museum researchers have illuminated biofluorescence in more than 500 species across the tree of life, with a particular focus on fishes and other marine animals.

This unique phenomenon, in which an organism absorbs light, transforms it, and emits it as a different color, has been uncovered in animals ranging from sharks to sea turtles to corals.

Now, new Museum research adds a terrestrial group to this growing list: birds-of-paradise, forest birds found across eastern Australia, Indonesia, and New Guinea whose males are known for their dramatic plumage and elaborate courtship displays.

“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,” Rene Martin, an assistant professor at the University of Nebraska-Lincoln who conducted this work when she was a Gerstner postdoctoral scholar at the Museum. “It seems fitting that these charismatic birds are likely signaling to each other in additional, flashy ways.”

Martin is the lead author of a study out this week in Royal Society Open Science that describes biofluorescence in 37 of the 45 known birds-of-paradise species. The project began about a decade ago, when Curator John Sparks, an ichthyologist, conducted a rapid survey of the Museum’s vast Ornithology collection for biofluorescence in birds, which revealed bright green-yellow fluorescence in birds-of-paradise.

Sparks’ initial work was continued recently by Martin and Emily Carr, a Ph.D. student in the Richard Gilder Graduate School. Using a specialized photography setup with ultraviolet and blue lights and emission filters, the team returned to the collection and found that biofluorescence is especially prominent in male birds-of-paradise, showing up on their plumage and skin in parts of their body that are highlighted during courtship displays: the inner mouth and bill, feet, and feathers on the head, neck, and belly.

“Observing and recording biofluorescence requires the use of bright, high-energy lighting and specialized longpass camera filters in a dark setting, making it a very complex task to perform in the wild,” Sparks said. “Luckily, we have access to a terrific collection of these birds right here at the Museum, with specimens representing all 45 described species of birds-of-paradise.”

Based on findings from closely related species, the researchers infer that the pigments in the birds’ eyes align with the fluorescence peaks they measured. This suggests that the “glowing” birds are adept at seeing biofluorescence, which increases contrast against dark plumage and possibly plays an important role in courtship and hierarchy displays.

“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.

The researchers note that despite there being more than 10,000 described species, very few scientists have investigated the presence and use of biofluorescence broadly across birds.

“Natural history museums are full of historical specimens that hold a wealth of information to address questions like this,” Martin said. “The door is wide open for more work in this area."