Variation in the Oxidative State of Collared Flycatcher (Ficedula albicollis) Nestlings and Its Association With...

Plumage coloration is widely recognized as an important component in intraspecific communication across different life stages. Although coloration received a lot of attention within the field of visual communication, we have little information on whether the oxidative state influences plumage coloration during early life. Our aim was to examine the variation of oxidative parameters and their associations with coloration of two different nestling plumage traits in collared flycatchers (Ficedula albicollis). We conducted spectrophotometric measurements on the nestlings' melanin-based wing coverts and porphyrin-based wing covert stripe and evaluated oxidative state by measuring the amount of reactive oxygen metabolites (ROM) and the plasma antioxidant capacity (OXY). At the nest level, oxidative state parameters differed in repeatability: ROM showed low repeatability, whereas OXY was not repeatable. This pattern suggests that variation in diet and other unknown factors in the study population may influence these measures, and that the two parameters may be affected to different extents by these underlying factors. We revealed that the oxidative state deteriorated with the progression of the breeding season. Individuals that hatched in late nests had a greater amount of ROM. Furthermore, oxidative state deteriorated with brood size, as ROM levels, but only in female nestlings, increased with the number of nestlings in the brood. Considering reflectance measures, we found that when low OXY was associated with high ROM, wing covert UV chroma increased. This may suggest that individuals who experienced worse oxidative state exhibited a shift toward higher eumelanin proportion in their melanin-based wing coloration. These findings underline the importance of oxidative balance for plumage color traits with diverse proximate backgrounds, and may encourage further investigations in the field of nestling visual traits.