Chicken are silkies and polish. They share the coop with some young ducks. Food is layer crumble mixed with cracked corn, oats and barley. Scratch occasionally and kitchen scraps. Suddenly a chicken will become weak and sit in the run. When I pull them out I find they have smelly poop on their feathers. They are very thin. Their keel bones are very prominate. I bring them in and try to nurse them back, but they slip away. What is going on? It is not all at once. I seem to have them dropping off one by one. The ducks are fine and no problems. No new birds have been added. The ducks were added over 6 weeks ago and were hatched from eggs in my incubator.