One of my hens is quite poorly and very underweight. She is 3 years old and a RIR/LS cross. She has been unable to fly/jump up to the roost for the past few days and this was what alerted me to her illness as she otherwise looks fine. She has really fluffy feathers so I didn't notice how thin she was until I picked her up. There is no sign of any injury or trauma, or lice or mites. She has access to food and water. Her poop is runny and smelly. Their food is fresh with no mould. I have now wormed her and brought her inside. Fed her scrambled egg and mealworms, added garlic to her food, given her vitamins in her water, and apple cider vinegar. She is eating but not a lot. Have syringed water into her mouth to make sure she is hydrated. What else can I do? The vets around here know less about chickens than I do, so no point in taking her unless she needs antibiotics. Her comb is nice and red, and eyes bright, no discharge from eyes or nares. No sneezing or coughing. She is listless and just sits there. I went into the coop today and another hen was dead in the nest box. She was a good weight with no signs of illness we had noticed, so a real surprise to find her dead. No predators have been. All my other birds seem fine. The only thing that has changed recently has been the addition of a new duck to our mixed flock of chickens and ducks about 3 weeks ago. I did not quarantine her as she came from a good breeder whose birds were all healthy. Wish I had now, but the duck is fit and healthy. Could she have brought a disease to the chickens that is not affecting her? Tomorrow I will scrub out the coop and dig over the ground they are on. Can they be poisoned by dirty ground? Are they dying of old age? Haven't had many eggs for a couple of months, but it is winter here and I expected them to take a break. I am at a loss to understand what has happened. Can anyone advise?