The set up: In the large pen: I have had 7 chicks that are 6 wks old, a 5 mo. old Orpington hen, and four 4 wk old chicks. The youngest 4 chicks we still bring in at night. All of these have been doing great together. We lost the Orpington and have had to separate out a chick that lost a wing in a predator attack yesterday. In the tractor: 6 more chicks of different breeds including 2 bantams. The new chicks vary from about 4 wks to 6-7 wks.. They were all sent together in one box for their comfort, etc. The question: I have read over and over 30 dys here on the forum. Got my Chickens for Dummies book and it says 2 wks. is good. In reading in the book about how chickens pecking order gets disrupted when birds are added or subtracted I thought maybe now is the best time since they've just lost the large hen and I've had to separate out a wounded chick as well. The birds are all for the most part about the same size. Perhaps I could introduce (with a temp fence in the larger pen) the largest of the chicks to the original chicks? Or intro them all within a temp fence? I have some concern for the Polish and the Mille Fleur D Ucle as they are smaller. We have had the newer chicks for just a few days shy of 2 wks. No evidence of illness other than treating them for cocci when we first got them.