Male birds of paradise can really put on a show. They aren’t just adorned with striking colors. They’re also known to use snazzy dance moves to woo potential mates. Now, it seems the flamboyant flyers have one more trick up their wing to heighten the drama of their displays. Under bluish light, many male birds of paradise have glowing body parts.
This type of gleam is called fluorescence (Flor-ESS-ents). It occurs when an object absorbs light at one wavelength and then shines light of a lower energy.
Fluorescence “is becoming more and more well-known across the tree of life,” says Rene Martin. She’s a biologist at the University of Nebraska–Lincoln. Martin has studied fluorescence in deep-sea fishes. Scientists have also found fluorescence in some amphibians and mammals and a handful of birds.
Martin went looking for fluorescent birds while working at the American Museum of Natural History in New York City. The museum has specimens of all 45 species of birds of paradise. Birds of paradise are found in the forests of Papua New Guinea, eastern Indonesia and eastern Australia.
Martin swept through the collection, shining a blue light flashlight over the birds’ bodies. That color light can prompt some animals to fluoresce. Martin wore yellow goggles that filter out blue light so she could see which birds gleamed green-yellow.
Of the 45 species, 37 fluoresce, her team reported February 12 in Royal Society Open Science. The ones that didn’t glow were closely related to each other. These birds of a feather evolved earlier than the fluorescent birds of paradise. The no-glow birds also appear drab to the naked eye and don’t perform fancy dances, Martin says. And unlike their flashier kin, they tend to mate with a single partner.
For the birds that do glow, fluorescence seems to help attract a mate, Martin says. Several pieces of evidence point to this.
For one thing, past studies have suggested that birds can see fluorescence, based on their eye parts. For another, male birds often perform mating dances in areas where they can soak up sunlight containing ultraviolet (UV) or blue wavelengths that kick off fluorescence. The birds’ glowing parts are often on or near parts of their body used in displays. And the fluorescent parts tend to appear against a contrasting background. For example, some male birds fan black wings around their faces. Against the dark feathers, a glowing mouth — gaping wide open at a female — can really pop.
Martin hopes to study live birds to confirm whether males’ fluorescence actually makes them more alluring to females.
Birds of paradise have caught the eye of plenty of scientists in the past, Martin says. But the discovery of their fluorescence is a reminder of how much we still don’t know. “Can you imagine all of the things that we still don’t know about groups of birds or any organism?”
Data Dive:
- Think about how birds of paradise use their glowing features. What other animals do you think may fluoresce?
- Look at Figure A. What wavelengths correspond to green-yellow glows in birds of paradise?
- What are some of the birds’ body parts that glow?
- Look at Figure B. On Parotia berlepschi, which part glows the brightest? How does this compare with its black feathers?
- Look at Figure C. How does the brightness of UV excitation light compare with the birds’ glow (the peak at 500 nm)?