They are growing their "real" feathers and the "downy" feathers are disappearing. They will look all scruffy and odd for the next few weeks until their feathers grow properly. It's a hard time being bossed around by all the older chickens and it gets really tough for any chickens that start to look like roosters, more about that below...
Check out Houdini now!
Is he a she or she a he?
It's still a bit it hard to tell. My guess is a "she".