I agree with @KikisGirls It is more likely that you are dealing with Cocci. Putting them outside exposes them to it in the soil. I would treat every bird you have. It doesn't hurt if they get treated and do not have it. Get some Corid, from your local farm store like Tractoe Supply. I use powder. It also comes in a liquid. You need to go get it and come back and tell us what you got because the dose will differ depending on the kind you get. Cocci kills fast. The Corid is listed for calves.