Three Muscovies have disappeared - poof! - gone. They were there this afternoon when I went out to feed everyone, but at dusk when I went out to close up the chicken coop, there were only four ducks accounted for. Ken and I tramped around with flashlights, but no luck. Strange thing is, there are no tracks of any predator-type animal in what snow is left, although there are large patches of snowless ground, enough that some animal could conceivably have come and gone without contacting snow. But besides that, if they were grabbed by some predator, unless there were three predators that all showed up at the same time (unlikely), after grabbing the first and taking off there should have been a ruckus and it would have been hard to not hear that. AND, there should be some evidence - bunches of feathers scattered around for example, but there aren't.
The other possibility is that they went off somewhere and as it started getting dark, they decided to sleep where they were instead of coming back to the poultry yard with the others. This is what I hope happened, and that they will show up tomorrow.