The tough guys! I often wondered why the Buffalo in Yellowstone have such huge necks. One reason is the searching for food in the winter. All day these behemoths bury their heads in the snow moving their massive heads back and forth. This gets the snow out of the way and gets them to the grasses deep in the snow.
Even with their size they are at a constant risk from predators. Energy is often expended running from possible trouble.
The life for the buffalo in winter is typical for all the other wildlife. Cold, wind, extremely limited food resources and difficulty getting around makes for great opportunities for some specific predators.