About two months ago we started our very first flock. We got 3 RIR's 2 leghorn's and this adorable grey chick who is now black with white speckles and has a white neck and head. Im not sure what breed he is? Then about 3 weeks after that we were given another 10 chicks. 5 more RIR and 5 plymouth rocks. Everyone got along great for the first 3 weeks. They were kept togeather and no one gave anyone a hard time. This weekend my husband and i finished the new coop and moved everyone in and i had started to notice some lost feathers on the youngest girls then. Not all of them but probably over half of them are missing lots of feathers now. Mostly off the center of the back and the chest. Tonight when i got home and checked on everyone the unknown breed chick has a large open hole in her back. It wasnt activly bleeding but it is very raw. I pulled her out and cleaned it up and set her up in a seperate cage with food and water next to the coop so she wont be lonely. I watched all the others interact for a while and decieded that it was one of two possible culprits. I just wasnt sure which one. So i took 2 of the older RIR out. (that is the two who i couldnt pick from) My plans are to let all injured parties heal then reintroduce the 2 RIR. Does this sound like the right approach? Does anyone have advice about if i should just keep the little one completely seperate from the big ones till they get about the same size? Just not sure what to do and want everyone to stay healthy and happy.