Hey,
Is there a certain time when your duck(s) keep closing one eye? Mine do this but only when their resting.
I read somewhere that a study revealed that ducks and other birds are able to allow only half of their body to sleep at a time. They normally situate themselves so that the 'sleeping' half is facing their flock and the alert side is facing the direction where possible danger could come from.
Does that sound familiar to you? Do your ducks do that? My aviary birds also do the same.. resting with one eye closed.
But if it's the same eye constantly and only the same duck(s) that do this then maybe theres a problem. It could be something trapped in the eye, in which case a trip to the Vet would help.
Do your ducks have deep enough water bowls? Ducks need to be able to submerge their heads and bills so that they can keep their nostrils, eyes and ears clean.
As for your ducks shivering and shaking. Mine also do this, but normally after a bath/preening or when their wet. It could be just the same as us shivering when we get cold. But after a few minutes, definately by half an hour they stop.
Mel X