We’ve always known birds of paradise are beautiful – but now, scientists have discovered a secret quality that the naked eye cannot see. You may have watched these brilliantly coloured birds fluttering across your TV screen, but you probably didn’t know they could glow.
The new research, led by scientists at the American Museum of Natural History and the University of Nebraska-Lincoln, reported that biofluorescence is more common than previously thought – being found in 82% of the known birds of paradise (Paradisaeidae) species.
Biofluorescence – a quality some animals have that allows them to emit light that humans cannot see – occurs when an organism (like birds of paradise) absorbs high-energy wavelengths of UV, violet and blue light, and re-emits them at lower-energy wavelengths of greens, yellows, oranges and reds. For birds of paradise, the study found that they absorb UV and blue light and emit a bright green-yellow glow.
Published in the journal Royal Society Open Science, the study suggests that the 'glow’ seen in the birds’ feathers is important for males establishing a hierarchy – taking 'dressing to impress' to a new level.
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How – and why – do birds of paradise glow?
The scientists behind the study think that male birds of paradise may use the biofluorescence in their reproductive displays – the dances that they perform to attract a mate. The birds use their brightly coloured feathers as part of these displays, so being able to glow gives them an added advantage that enhances their performance.
But there could also be a geographical reason for their glowing. “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,” said Emily Carr, a PhD student at the Museum who co-led the new research.
This discovery matters because birds of paradise rely on what they see to find and attract mates, and their hidden glow could be a key part of what they see during their dances. In fact, the study found that pigments in the birds’ eyes actually match the fluorescence in their feathers. This suggests birds of paradise see a different colour spectrum to humans, allowing them to spot these biofluorescent patterns our own eyes can’t pick up.
“It seems fitting that these flashy birds are likely signalling to each other in additional, flashy ways,” said Prof. Rene Martin, assistant professor at the University of Nebraska-Lincoln.
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How rare is biofluorescence?
Museum curator and ichthyologist Dr John Sparks has previously studied this phenomenon. He identified biofluorescence not only in birds of paradise, but in hundreds of species, including corals, fish and turtles.
His past research found that birds of paradise had this biofluorescent gift – allowing them to perform a kind of light show – unlike other colourful species such as bowerbirds and (adorably named) fairy wrens.
“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.
To explore this further, Martin and Carr used a dark room – like those used for developing photographs. First, they collected specimens dating back to the 1800s from the Museum’s collection and then shone blue light onto them.
By using camera lenses to filter wavelengths, they unveiled the hidden glow of the feathers – unlocking the secret world of colour usually only admired by other birds.
Main image: biofluorescence seen on an emperor bird of paradise (Paradisaea guilielmi)/ Rene Martin
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