Help! Last night one of my orpingtons didn't go in to roost. She was just sitting outside on the ground. We checked her and put her on the roost. We couldn't find anything wrong with her. This morning she was dead. I have 16 hens and now half of them seem "off" this morning. Very slow moving, not eating, drinking water slowly, and just laying down. All the combs seem bright. Nobody looks sick but something is very wrong. Does anyone know what I could be dealing with?