Age-Related Differences in a Carotenoid-Based Coloration Trait are Due to Within-Individual Changes in Great TitsParus major

Abstract

Adult birds usually display brighter plumage coloration than younger individuals. This difference may be either due to selection against less coloured yearlings or to an increase in coloration after their first complete moult. In this study, we examined age-related differences in carotenoid-based yellow ventral coloration of Great Tits Parus major. Cross-sectional analyses at the population level showed that older males are in general greener and more saturated in colour than yearling individuals. Longitudinal analyses using birds captured in subsequent seasons confirmed within-individual changes in coloration with age. Such increase in coloration might be the result of the development of better foraging skills with age- and hence, the individual ability to obtain enough carotenoid-rich sources at the time of moult-, or consequence of other factors indirectly associated with age. However, we cannot rule out the possibility that other factors (such as directional selection against less coloured individuals) operate additionally at the population level.