What do foxes do during the winter?

I'm not really sure I understand what your question means, did you mean why or how? I'll take a guess at a general answer. Winter affects all animals by the cold weather, but native animals are adapted to it, so they grow thicker coats of fur or fatten up for winter to hibernate. Foxes don't hibernate, so they are one that grows thicker fur. More important effect is how the weather changes what foods are available. Lack of food, not temperature, is what sends most migratory animals south. Animals like foxes are predators that don't migrate and they eat mostly rodents and rabbits. Some rodents hibernate in the winter, so they are harder for foxes to find and deep snow might make hunting more difficult.