New research finds fluorescence in feathers of long-eared owls

While there is an astounding variety of physical differences in wildlife that humans can easily observe, new research from Drexel University’s College of Arts and Sciences reveals that there is likely even more variation hidden from our perception. In a study recently published in The Wilson Journal of Ornithology, the researchers report their discovery of fluorescent pigments in the feathers of Long-eared Owls, that can only be seen by humans with the help of ultraviolet light.

The study, led by Emily Griffith, a PhD candidate in the Biodiversity, Earth & Environmental Science department, shows that fluorescent pigments in the feathers of Long-eared Owls can vary within a population and that variation gives clues as to why the owls have these special pigments. 

To conduct the research, the team used a fluorometer – a device that measures fluorescence or light that is emitted after absorbing radiation such as UV light – to measure variation in the amount of fluorescent pigments in the feathers of Long-eared Owls migrating through the Upper Peninsula of Michigan in the spring of 2020.

“We are only beginning to describe fluorescent pigments in birds and other vertebrates,” said Griffith. “Although describing what species they are present in is important, in order to understand what their function is we need to also describe how they vary within a species like the Long-eared Owl.”

Griffith noted that in many bird species, pigments are used by males to attract females, which is why most people think of the males of many bird species as being more “colorful” than females. But the research team suspects that the function of these pigments is not necessarily related to sexual signaling.

“Our study shows that female Long-eared Owls have a much higher concentration of these pigments in their feathers, challenging a common misconception that colorful plumage is a ‘male’ trait,” said Griffith. “Moreover, this trait doesn't follow a strict binary – the amount of fluorescent pigments in these owls exists on a spectrum where the amount of pigment is related to size, age and sex all together.”

The research team explained that fluorescent pigments have likely been used by animals for a long time, but technology has limited the study, or even acknowledgement of the pigments, until very recently. Griffith and her colleagues’ interest in the study stemmed from the fact that many owl researchers use these fluorescent feathers to age birds in the field, since the intensity of the fluorescent glow dissipates with time. Griffith added that researchers are just beginning to understand these “hidden” traits in Long-eared Owls and other birds – what the fluorescence means, where it can be found, how it got there and why it’s there.

“So little is known about fluorescent pigments in bird feathers and owls aren’t the only ones with fluorescent pigments,” said Griffith. “So, it’s a really exciting time to be interested in studying bird plumage.”

Read the full study here: https://www.tandfonline.com/doi/full/10.1080/15594491.2024.2444031.