Part of the abstract:

Recent findings on the abilities of birds to see in the ultraviolet (UV) spectrum have expanded questions about plumage coloration to include the luminescent characteristics of bird plumage, including fluorescence. Yet little is understood about the function of fluorescent pigments, and very few studies have attempted to describe their distribution throughout a population. In this study, we used a fluorometer to measure variation in the amount of fluorescent pigments (e.g. porphyrins) extracted from the secondary coverts of Long-eared Owls (Asio otus) migrating through the Upper Peninsula of Michigan in the spring of 2020 (n = 99). We found that age and sex were the strongest predictors of fluorescent pigment concentration, wherein older and female birds had the highest fluorescent pigment concentrations.

I understand this is not your regular Superb Owl post, but I found it mighty interesting!