Blog editors note: The writer of "Keeping Backyard Bees" is in a southern state. I doubt very much our bees in Wisconsin were out gathering pollen in December. The only bees I have seen outside the hive are dead ones in the snow that could not get back to the hive during a voiding flight taken on a bright sunshiny day. However, at the end of this article are some good pointers about checking your hives for the lack of food stores.
Here in the link to read about 'winter' pollen gathering.