Feather plucking

I have 24 ten week old chicks. 6 of which are Polish chicks. This is my third flock. 22 are hens, 2 are silver leghorn roosters, all same age. Suddenly, the Polish are getting their heads plucked, one at a time, now I have three living in my shower, and outside during the day, They are getting extra protein to get their feathers to grow. Must I isolate all the polish in a separate pen or what? I have aracuanas, silver flecked, rhode island reds.. Other than sitting outside the pen to see what is going on, what can I do? They have plenty room, hen house, enclosed coop, free access to feed, with lettuce, fruit, etc., treats.

 

thank you - guess I have to build another pen.