One chicken this morning seemed very sluggish and quiet. When I first saw her she was lying on her side. She got up, but with difficulty, and seemed to have little interest in following the group out side. The chickens have been going outside each day, under supervision. Most stick close to their cage. A few have nibbled some grass and weeds(we use no pesticides on the grass and weeds, no fertilizer). Other than her holding her beak open, I see nothing else other than a depressed, quiet attitude. It was very hot yesterday, but most of the chickens stayed in the shade and seemed completely unbothered by the heat. They ate and drank well. Today it is suddenly quite cool. Their cage is in a shady garage, but I can open the garage door to let in sun or to shade it however much is needed on a given day. The chickens are about 3 months old now, of a very good size, and appear very healthy other than this one. They were vaccinated for Mareks at the hatchery. I believe they are moulting as some feathers have dropped in the pen and some have downy feathers, which I think are new feathers. Their feathers are otherwise glossy and healthy looking. They get medicated Layena Flock Starter. No other chicken seems to have the same symptoms as this one. I have 50. None of them have shown any sign of any problem. All perky, lively and very interested in their food and water. We had a nice 'chicken enrichment' yesterday with all gathering around to peck at a thread hanging off my blouse, LOL. They get Layena, all they want, fresh water, and fresh alfalfa cut from our pasture, also not treated with pesticide or fertilizer. Occasionally I give them other treats, such as lettuce and ground sunflower seeds (no shells). I have seen them pick up bugs and flies, too. Their waterer is rinsed and cleaned every day. They are bedded on McCrumb - kiln dried white pine shavings that are crumbled for more absorbency. Since the other chickens were bumping into her (accidentally, they actually appeared for all the world to be inquisitive, even concerned about her), I left her in the cage by herself. She did not seem to care that she was alone. I thought it might give her a chance to rest, but I just have an uncomfortable feeling that this is very not good. She stands with her neck pulled in short, and her tail down. She doesn't seem to notice the other chickens moving about. Many of them are sticking close to the cage (they usually do that) and actually appear to be clucking to her. No signs of a dirty bottom or of different droppings. I can take her to the vet later today if she does not appear to be any better. I sure would like to know what is bothering her.