07 December 2012

Friday Field Notes: Winter's Other World

There's a whole other world out there that only exists in winter. The arrival of snow literally creates an entirely new habitat not found at any other time of the year. Naturalists know this place as the "subnivean environment."

While we might just see snow as powdery white stuff that accumulates as winter goes on, there is actually a lot happening underneath the surface. And indeed, the word subnivean, which means "under the snow" in Latin, suggests just that. As snow accumulates, it undergoes a variety of transformations: it compacts, melts, and refreezes. All of these changes form what we commonly think of as the snowpack. The snowpack can contain a variety of different layers, some hard, some soft, some deep, some shallow. These layers provide opportunities for small animals to create burrows, tunnels, and other structures that would be much more difficult to maintain in the soil, which is typically frozen throughout the winter.

Small mammals, like mice, voles, and shrews, likely could not survive outside of the subnivean environment. In addition to providing physical space for them to live in, the subnivean provides critical insulation. While the world above the surface is exposed to high winds and temperatures in the negatives, life underneath the snow remains a relatively cozy 32 degrees Fahrenheit! The other benefit of living in the snowpack is the protection it offers from predators.

Of course, these small mammals aren't totally safe. Have you ever seen this?

A fox dives into dinner head-first.

Foxes - as well as coyotes and some owls - are capable of hearing the movement of rodents underneath the snow. They wait patiently, honing in to the animals' exact location. And then, they pounce (or in the case of the owl, swoop). Extraordinary, no?

And then of course, there's this:

A marten emerges empty handed.

American Martens, like most other weasels, have never been afraid of digging in and getting a little dirty (or snowy?). Instead of listening for rodent movement and using stealth to catch their prey, they rely on power and speed to ramble through the snow and grab critters.

Next time you're out skiing or snowshoeing, imagine all the things that are going on beneath your feet! The snow isn't just snow; it's another world.

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