how many hens do you have for your drakes? if you don't have enough hens, the drakes will certainly escape to look for a mate/territory. muscovy can be really tame, but they're still good to look for the call of nature..
do you have a big pond? they don't actually have to have a big pond, but all ducks, even tree ducks will leave if they think they can find a pond.
if you're yard has clean water, good food and is safe, birds are birds and will still try to wander. mine absolutely love to escape and visit the...