Waterfowl generally don't succumb to internal parasites, but there are (rare) times when they come down with it, either due to ingestion of a secondary host of the worms like frogs, or earthworms, or sometimes when they're kept in filthy conditions that allow the worms in the soil to reproduce to the point where it can infect the birds quite easily.
If you happened to find worms in their feces, or found an excess amount of worms in their feces in a fecal float, with additional clinical signs to back the finding up since some birds can have above normal worm eggs amounts and still act/live fine. As a broad-spectrum dewormer, you can use either Valbazen or SafeGuard.
The SafeGuard Liquid Goat Dewormer dose is 0.23ml per pound once a day for five days. ) :