Muscovies can and do fly VERY well, especially the hens. We have some wild ones that live near here and like to visit and eat scratch that I put out for them. One of mine, a hen, decided, after staying in our yard for months, that she wanted to join the wild Muscovies. She flew away one day and didn't come back until recently. Over 2 months!! I thought something got her. I had never clipped her wings, cause she had been staying around our yard and just flying away some during the day and always coming back! Well, anyway, she came back and brought three little babies with her. I never could catch her though. She has been with the wild ones long enough that she doesn't want to be caught. Sometimes she is here, and some days she isn't.
So, I know they can fly. We have seen her many times take off and just fly away, over the trees, across the cow field across the street from us, etc. I've seen the wild ones do the same thing. Especially the hens, as they are lighter, but the wild drakes fly pretty good too. It just takes them longer to get any height, but they can and do fly.
Also, I agree with training your ducks to go into a safe and secure place at night. I have four pekin/swedish mixes that I got about 2 1/2 months ago. They were already 4 months old when I got them. The guy that had them didn't let them free range. They were in a hutch type thing and never went anywhere. Once I got them, I put them in a pen, where they can be out all day. At dark, I go out and herd them into a very large plastic airline dog crate and shut and latch the door so nothing can get them. The pen is an open pen right now, cause the fence is only 4 feet tall so I can't walk around in it if we put a cover on it. It is temporary though, as my DH said he would build me a new coop and run. Anyway, I always put them up before dark. Well, once in awhile, if we are gone, it is just after dark when I put them to bed. Usually, they are NOT in the crate, but laying around near it. Last night, it was late when we got home. It was the first time they were ALL in the crate. All I had to do was shut and latch the door. They finally understand that that is where they go at bedtime.
When I go out to put them up at night, I tell them all right duckies, time to go nite nite. They usually all go directly to the crate once I am out there to herd them in. I figured if I use the same tone of voice and say the same thing each night, it will train them to go to their crate. So far, so good! LOL I was surprised and happy to find them all IN the crate last night on their own. I feel like I am making progress with them.
Good luck with your ducks!
Post pics when you get a chance. I love muscovies!
Kathy