After completion of post-juvenile moult, readily sexed based on the colour of crown feathers. A few birds, probably females, are more intermediate, showing slight orange. Svensson (1992) gives some further clues concerning such birds.
Male, 1cy, November. Underlying crown feathering bright orange. Note that the orange feathers are often concealed by yellow, and feathers must be separated in order to examine. [TJ4127]
Female, 1cy, November. Underlying crown feathering all lemon yellow. [TJ4133]