Data from: Variation in the oxidative state of collared flycatcher (Ficedula albicollis) nestlings and its association with their plumage coloration.

Plumage coloration is widely recognised as an important component in intraspecific communication. Although coloration received a lot of attention within the field of visual communication, most studies focused on adult birds, thus our knowledge on the relevance of plumage coloration in early life stages is still scarce. In particular, we have little information on whether the oxidative state influences plumage coloration during this period. 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’ wing coverts and 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 parameters differed in repeatability, suggesting that ROM is more strongly shaped by genetic factors, while OXY is more influenced by environmental and individual-specific factors. We revealed that the oxidative state deteriorated over time, because individuals that hatched in late nests had a greater amount of ROM. Furthermore, ROM increased and oxidative status deteriorated with brood size, but only in female nestlings. In wing covert, we found that if low OXY was associated with high ROM then UV chroma increased. These results suggest that individuals who experience worse oxidative state expressed less developed coloration. These findings highlight the importance of studying visual signals and their determinants in early life stages, and encourage further investigations in this field.