For birds, a delayed postjuvenile moult may have carry-over effects on Darwinian fitness, as acquiring late the adult plumage can interfere with the protective or signalling functions of the plumage, or with the scheduling of migration.
@jpereztris.bsky.social #sylvia_atricapilla

The relationship is robust because it comes from a study of 26 Iberian populations of blackcaps, which face high parasite prevalence from very early ages, spanning a broad range of environments.