I had a small brooder pen made out of chicken wire sides, beneath nesting boxes, but it is really too small. I'm starting to really worry about how long I'm going to have to wait to introduce my chicks to the big girls. There is a 9-11 week difference between them. December chicks and Feb-march chicks. I am only keeping 6-7 out of 15 new chicks, but even with triple the space, the brooder is only about 1.5x7 feet enclosed, 2 feet high. How long can I keep them in there, for their safety? I've been letting them out during the day while the big girls are in the run, but I've read on here they have to be housed separately for 16 weeks?? How do you do that without building another coop?