Hot on the heels of the 2 weeks comparison montage, I give you the 3 weeks one:
The increase in size since the previous week is not that obvious in this shot, but the change in posture is, and there is some feathering around the face.
The trio, when not asleep, are a lot more mobile and adventurous. For the first time, at the beginning of this afternoon, they all went out exploring outside the nest box. Only one had done it sofar, for about 2 minutes yesterday evening.