Discussion
We hypothesized that offspring and adults not only display similar
colourful traits but that these traits might also have a correlated
signalling value across life-history stages. Indeed, as has already been
suggested (Johnsen et al. 2003; Jacot & Kempenaers 2006; Morales &
Velando 2018), we found that certain colour components of nestling
yellow breast feathers reflected body mass in the 3-year period. This
pattern was particularly relevant for UV chroma and total brightness.
Hence, these traits could act as condition-dependent signals beyond a
sexual selection framework, around which most previous work has focussed
(e.g., Senar et al. 2002; Hidalgo-Garcia 2006; Doutrelant et al. 2008,
2012; Ferns and Hinsley 2008; del Cerro et al. 2010; GarcĂa-Navas et al.
2012; Midamegbe et al. 2013; Ferrer et al. 2015). Furthermore, our
approach allowed us to explore the potential of the three colour
components as quality signals both within nests and among nests
contexts.