I have 9 Buff Orpingtons who are almost 3 weeks old, 4 RIR (almost 2 weeks) and 2 Ameraucanas (almost 2 weeks). They were introduced slowly about a week ago and have done great...until now. I noticed one of the RIRs is missing some feathers/down on the side of her neck. Skin looks irritated. Our chicks are brooding inside the house in a 2x4 metal trough. One side has 250w red lamp. Plenty of food and water. They're definitely running out of room though so I'm working on rigging up a larger space until my husband gets their coop and fencing finished. I suspect one of the Buffs is pecking on her but I don't know which one. I spend A LOT of time with them...observing, hand feeding, talking to them. Haven't noticed anything unusual so guessing it's happening at night. Just separated her by putting chicken wire down part of the brooder. She hates being by herself and was frantic so i put two other RIR with her. They're all pretty miffed to be separated. :/ gave each side a plate of sod to hopefully keep them busy.