Take multiple stool samples from the pen floor, mix them thoroughly and have the vet do one fecal float for the pen. That will save you a lot of money, should be $25 for one not $100 for four. If any one of the birds have worms or cocci they all need to be treated at the same time.
If they don't find any worms or cocci, ask for a gram scale for bacteria.
Excellent advice!
-Kathy