Hi Arthur, we caught a very similar looking bird on the Gower Ringing Course last weekend. In Blackbirds the head can be the last part of the bird that undergoes the post juvenile moult so the body looks adult-like (and black in a male) whilst the head can still be very pale sandy brown as in the two individuals pictured. This will change quite rapidly over the next week or two when the head will catch-up and they will look quite normal again.