I had a building collapse under snow load last winter (late December). While moving the turkeys that were in it, one of my White Holland hens flew out and landed on the greenhouse roof. When I moved the rest of the turkeys and went to get her, she was gone. I searched for a few days, no sign. We had a lot of snow last winter, with some major blizzards and temps close to 30 below. I finally accepted that if she didn't freeze to death, predators got her. Then in late Feb a neighbor called to tell me that there was a white turkey hen in her yard. Somehow my girl found food and made it through on her own. Her weight was good and she looked very healthy.
A bigger concern is that sometimes the bunnies hunker down in the winter and owls get hungry. A Great Horned Owl will take a full sized turkey out of a tree. I keep mine locked up in the winter.