Fluorescent pigment concentration correlated with age, sex, and size in Long-eared Owl ( Asio otus ) plumage

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 pig­ ments (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. We also found a significant positive relationship between fluorescent pigment concentration and weight in males and small females; however, larger females had no correlation between size and pigment concentration, indicating a potential saturation point for fluorescent pigments in feathers. While we conclude that although fluorescent pigments have the potential to serve as a communicative signal of age, sex, or size, we also acknowledge that these pigments could serve in a function unrelated to signaling, such as heat conserva­tion. More research on these fluorescent pigments and metabolic path­ways that lead to their production and deposition in feathers is needed before we can ascribe them a definitive function.