How big is your pen? If they are overcrowed they will peck each other or if they are not getting enough protein or if they are bored they will do it. (search site for more info) If the birds are bleeding you do need to get them away from the others, they will wound each other very badly, even in a couple of hours. If you can't bring them in then you do need to set up a divider, use a board or wire or something. You also need to put some pine tar on the bare spots ASAP before they learn that feathers taste good. Pine tar is in the horse section of your local feed supply store. It taste bad and will stop the others from pecking, it will also help heal the wounds. You do need to put enough that if they peck they will get some on their beaks. If you do this before they kill each other and before it becomes a habit, then you could try to introduce them back together at a later time. Even a small pen can be divided.