Pekin do well in the cold, though they miss their water horribly, i try to maintain some around for them but being they are part of a scovie flock i have to mind for them.. they love mud, mine wait for a spray from the hose, sadly they don't get why it doesn't run anymore lol.
My calls often swim in the very cold, now my scovies are not so winter happy, i have actually stopped allowing containers that they can get into to avoid them freezing themselves.. and yes i have had that happen, they are not as waterproof as mallard derived ducks.
If the run is predator proof they will choose whether or not to take shelter, i wouldn't worry about it. The biggest problem with leaving ducks out is them becoming someones dinner if they have shelter and protection they will take it when they need too
Ducks just need options, beyond that i...