Background: Plumage coloration is important for bird communication, most notably in sexual signalling. Colour is often considered a good quality indicator, and the expression of exaggerated colours may depend on individual condition during moult. After moult, plumage coloration has been deemed fixed due to the fact that feathers are dead structures. Still, many plumage colours change after moult, although whether this affects signalling has not been sufficiently assessed.
Delhey, K., Burger, C., Fiedler, W., & Peters, A. (2010). Seasonal changes in colour: a comparison of structural, melanin- and carotenoid-based plumage colours. PLoS ONE, 5(7), 1 - 14. https://doi.org/10.1371/journal.pone.0011582