I keep a top on my brooders. I have two -- the first is a large plastic tub; the second a large wooden box. Both have screened tops since I have cats. When the chicks are 3-4 weeks old and really start flying, they go to the larger brooder. It's in the basement so I just let them fly around until I'm ready to go back upstairs. Really fun to watch -- the friendly ones usually fly to my shoulder as they see me as one of their perches.
