Welcome! I don't have ducks. I feed PFR to my chickens and I remember someone's review that stated it didn't have enough niacin for water fowl. I'd put them on a supplement asap. Best of luck!
Calls do not require as much niacin as other breeds, so the niacin content in the feed should suffice. Adding extra niacin into their diet, however, would not be a bad idea.