I have a BSL (18 months old) that came out of the coop this morning along with 14 other chickens. I threw out a scoop of chicken scratch and they all started scratching and eating. Everyone was fine and in good shape. 4 hours later I look out of the kitchen window and one of my BSL's is lying on the ground dead. What? I went outside to check on her and the other chickens and found nothing wrong. All the chickens are acting normally and I inspected the dead chicken from top to bottom. Nothing that I could see had killed her. I'll be watching out for the other chickens just incase there is a virus or something going on. Any suggestions?