Fungal infections of the respiratory system can cause that behavior. There are other diseases too that cause that behavior also, but I think most of this behavior absent other symptoms can be fungus. Hot humid weather, moldy conditions, bad feed, leads to fungal problems for chickens. I just found a whole bag of scratch in my shed ruined because of mold. It got a bit hot and moist and that was it. Whole bag is dusty looking and smells. Glad I was paying attention before I gave it to birds.
Watch out in summer months because heat and humidity can mold your bedding, your feed, etc. Birds can easily become infected. Hard to cure.