I've never de-wormed my birds, unless I see worms in their poop or if they are showing symptoms similar to a worm infestation I feel no need to worm, waterfowl are generally very healthy birds that rarely have problems unless there is poor management practices involved, so unless they are walking around in there own feces all day and not being able to bathe you should be fine. Everyone has there own opinion on this topic so its your choice, some people send in waste samples to have them tested for worms before taking action, that's another option for you.