Yellowstone in winter is an incredibly raw and harsh place. The wind whips as temperatures reach well below 10 deg daily, with extremes into -50. Many bison in the Northern herd follow their ancient migration path out of the park and towards the Paradise Valley. The Southern herd is a bit different. Many bison leave the West side of the park, and a number of them remain in Yellowstone's high-elevation and harsh interior for the winter. They heartily eke out an existence near Yellowstone's many geothermal features -- because of the steam, there is less snow and the bison can more easily eat grass. I photographed this behemoth of a bull bison on a -28degF day in January. As the steam rose from the geothermals, it stuck to each hair and immediately froze. This is how we see a frosty bison -- something that is completely unique to Yellowstone.