The birds of paradise not only captivate with their plumage and dances, but they also shine in the darkness in an unexpected way: through biofluorescence.
A recent study analyzed 45 species and discovered that almost all of them exhibit this phenomenon, with green-yellow tones that could play an essential role in courtship.
Visual signals are fundamental for communication in animals. In birds, the vibrant colors of feathers are often crucial in courtship and reproduction.
However, this is not the only important characteristic in the mating processes. Previous studies have shown that some birds also use biofluorescence (when certain parts of their body shine under ultraviolet light in the darkness) as an additional signal.
Revealing research on birds and their glowing feathers in the dark
In a study published in the journal Royal Society Open Science, scientists analyzed 45 species of birds of paradise. The researchers used bird skins preserved at the American Museum of Natural History (AMNH) in New York, one of the most comprehensive ornithological collections in the world.
They examined specimens of all known species of the Paradisaeidae family. They analyzed both males and adult females of 45 species, except in the case of Parotia berlepschi, where only males were studied due to the absence of females in the collection.
They discovered that almost all of these birds exhibit biofluorescence (37 species from 14 genera). To detect biofluorescence, they used a method based on excitation with manual blue lights in a dark room. They used long-pass filter glasses to block the excitation light and observe only the fluorescence emitted by the feathers.
If a specimen showed signs of biofluorescence, it was moved to a completely dark room to capture detailed images and analyze its spectrum of fluorescent light emission.
These birds mainly inhabit the dense tropical forests of New Guinea, some nearby islands of Indonesia, and northeastern Australia. They are known for their extravagant plumage, which includes vibrant colors, metallic iridescences, and ornamental feathers in unique shapes, such as long filaments, fans, and spectacular crests.
Males usually display a combination of velvety blacks, emerald greens, intense yellows, electric blues, and metallic purple tones, while females have a more discreet plumage, in brown or beige tones, which helps them blend in with the surroundings.
Biofluorescence in courtship
Biofluorescence did not appear in the same way in all birds. In males, biofluorescence is manifested in the feathers and skin used in mating rituals.
Depending on the species, the glowing areas include the inside of the mouth, the beak, and the feathers of the head, neck, belly, and crests. In females, the glow is mainly observed on the chest and abdomen.
The color of the biofluorescence is green or green-yellow, with a more intense glow at certain wavelengths of light. The study results suggest that males likely use this biofluorescence to highlight their visual signals and enhance their success in competition and courtship.
These birds live in tropical areas with intense sunlight, which makes their biofluorescent feathers stand out more. Additionally, in the forests where they inhabit, light filters in different ways, which can enhance this effect. In fact, it is sunlight that excites the fluorescent molecules (fluorophores) in their feathers and skin, causing them to emit visible colors under certain conditions.
Unlike other birds that can see ultraviolet light, it is believed that birds of paradise can only detect colors within the visible spectrum. However, their eyes have special characteristics that allow them to clearly see biofluorescence, helping them distinguish the most attractive males.
For example, they have pigmented oil droplets in their eyes, which allow them to filter and perceive colors in a different way than other vertebrates.
Researchers believe that many more bird species could be biofluorescent, but further research is needed to fully understand their role in evolution and visual communication in birds.
Cover photo: René Martin
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