Mistle Thrush chick or adult?



The mistle thrush nest I discovered 3 weeks ago has chicks and this one, at least I think its a chick, is considerably larger and more bold than the other two. I think its nearly ready to leave? But am I mistaken and its actually the adult sitting tight? I realise there are some whispy patches of downy feathers on its head but could they have just come from the other chicks and stuck on? Chick or adult?