This is part of a 3 part Yellowstone documentary that I saw. Freakin amazing what the animals there go through each year to survive. Its on netflix, and worth watching. This is one of my favorite scenes
The layer the mice are chillin in is the crazy ass, subnivian zone, air space above the surface of the ground and beneath the snowpack being held up by pillars of ice crystals. Its like a whole world that only exists in winter.