I have a chicken, roughly 18 weeks old, who seems very weak. It can barely hold its own weight and usually just sits. I felt it's legs and it feels like there is hardly any leg muscle, and is pretty boney all over. Also does not hold its wings up which in combination with sitting a lot, the tips of its wings have kind of curled under. This started maybe a week or so ago. It is alert and eating. I separated it today as he was getting picked on. I did have another bird die totally out of the blue the other day. She was fine one day and dead the next. Another went missing so can't be sure if it was sickness, predator. Does this sound like Maerks? All the other birds are currently fine.