We have seven similarly aged silver appleyard ducks, and we also had a very warm fall. Then winter hit--we have not been above the single digits F during the day, and the nights are as low as -10 for over a week. We also have about 10 inches of snow on the ground, and we've had some very blowy days (40 mph+).
I'm pleased to report our ducks have acclimated well. They miss their foraging time around the property, but their run is covered with a thick layer of straw that gets fluffed daily. 2.5 sides of the run are banked with straw bales providing a windbreak, and they have an area under their elevated duckhouse, which is very protected for daytime naps.
They have free-choice pellets and some cracked corn in their run, along with water in a heated bucket. We feed them a soup at around 3:45 in the afternoon, and then we've been locking them into the duckhouse just around dusk each evening when the temps are below 0F.
The duckhouse is roughly 4'x8' with a thick layer if pine shavings and straw on top of that. We fluff the straw daily and add more as needed. We do not give them any food or water in the duckhouse. The duckhouse is not heated, though it does have power.
In the morning we give them soup, top off their food, change out their water, and inspect everybody.
They seem pretty happy all things considered.