Hi Keith, nice image of a particularly strongly coloured juvenile.

Hi Peter, this individual was the only one in a flock of twenty birds which showed such strong colouring.

These adult summer plumage-traits in juveniles are the rule of thumb when it comes to Dunlins (the dark belly-patch), but obviously much more rarely seen in juvenile Knots.
One for the folks studying how closely related the individual species in the genus are to each other.

Well documented here.

Regards
Peter

Many thanks, KEITH and PETER, for highlighting
this Juv.(!) plumage,
which I till now would consider (granted...)
fading Adult.

Noticeably, SVENSSON confirms that colour of juv.
underside rarely may approach summer adult's.
__________________
DANSK

Tak KEITH og PETER for ligesom SVENSSON at påpege,
at farven på Juv.s underside kan nærme sig sommer
Adults.

VH / BR ........ C.