I was watching my goslings and ducklings after I put their water in. They submerged their heads etc. 2 out of the 4 shook their heads and slung whitish stuff out their mouth. Same 2 had clear mucus like stuff drip from their mouth when I picking them up. All 5 sneeze off and on. Sick? Vet check? Help.
Do they have limited access to water? They need to be able to submerge their beaks to clear feed/debris from their nostrils. If they are eating, drinking, defecating, and acting normally, I doubt if you are dealing with a health issue. Sounds like more of a husbandry issue.