I'm with Wildone on this
It's amazing how many bald female and some male ducks we get in during the summer. It's caused my over amorous male ducks gang raping others. If not treated, the sun (when we get some) dries out the skin on top of the bald head and draws the eyelids up so that the duck cannot close its eyes.
So far the only remedy we have is to cut the skin above the eyes and keep the area moist to allow the eyelids to close.
If you don't then the ducks go insane from lack of sleep and die!
So if you do see a bald duck then report it and hopefully it can be rescued before it gets sunstroke or worse.
Jo