I have a buff orp, 2 RIR, 2Barred Rocks, 2 Golden laced wyandotts, and 2 black australorps. They are all about the same age within 1-2wks. I got them middle july they were 9-11 weeks then. They are all growing in size except australorps. One especially is quiet small. The other one is mixed with cochin and is a little bigger but the others are eating her feathers on her back by tail. Do australorps grow slower? They appear as healthy as the others and eat everything they are given. this is my first go around with chickens so I don't know much yet. still learning and asking lots of questions.