Juveniles

Hi- this is a rough guide

BTs fledge in about 22 days and are then sulphur-cheeked for about 120 days.
They can be aged in autumn as can many passerines by the greater covert moult / growth which is visible in the field with a good view.

Adults have normally completed a body moult by October and then look fabulous- time varies depending on geography- as northerly birds possibly breed a little later .

S

At this time of year the "scruffy" looking birds can often be overworked adults feeding young in the nest although breeding seems a little late in our locality.

Thanks for the replies S and Pete. I have a few scruffy looking blues, coals and great visiting all year round, slightly smaller than their contemporaries. They seem to be ok though, certainly not slower or disfigured in any way, so just wanted to reassure myself that they aren’t diseased at all. I’ll try and get a few pics of them