Subnivean zone: the secret world of mice living under the snow

Beneath the snow, a hidden world of mice are wide awake. Here's how it works. Once snow is about six inches deep, it holds the ground steady near 32 degrees, even when the air above is far colder. It's the subnivian zone, where mice, voles, and shrews stay active all winter. But predators know it's there. Red foxes dive headfirst into the snow. Great gray owls punch through the crust to grab voles up to 18 inches down. The snow looks quiet underneath. It's anything but.