I noticed today that one of my Dixie Rainbow chicks is standing around in corners puffed up with its tail down. I watched it for a while, and it's eating, drinking, and pooping normally, but is acting semi-lethargic. It's not sleepy-acting or anything, but it will walk a while and then stand still, puff up its feathers, and keep its tail way down. Dixies are meat birds, so they have big thick legs, but this one's are smaller even than the egg layers' legs. But if it's legs were weak, wouldn't it sit down instead of standing up? This one is a lot smaller all around than the other Dixies that are the same age (I think maybe it's like a runt). It's not cold - the temps have been up in the 80s and 90s lately - and they've got food and water all the time. It's the only one doing this and it just started (that I've noticed) today. What could be wrong with it?