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  • Sara Thompson

Dive into the Subnivean Zone

By Sara Thompson

Special to the Enterprise

Have you ever watched a fox jump and dive headfirst into the snow? It can be an amusing sight, but the predator is actually hunting for its prey under the snow. Each winter, under the snowpack, a specialized climate is formed called the subnivean zone. This is where many small animals will spend their winter, protected from both the elements and hiding from predators.

Subnivean comes from the Latin words for under (sub) and snow (niveus). As snow falls and accumulates it will begin to insulate the ground beneath it, keeping it warmer than the air above. The warm ground will heat the lowest level of the snow, transforming it into water vapor, and creating a small gap between the ground and the snowpack. When the water vapor will refreeze on the “roof” of the space, creating an ice layer, giving structure to the space and further protecting it from the cold. The temperature in the subnivean zone is around 32oF, much warmer than the surface temperature that drops well below freezing.

The subnivean zone is home to an assortment of small creatures including mice, shrews, voles, and more. Small mammals lose heat much quicker than larger ones and are too small to handle the growth of a winter coat. During the winter small mammals, such as rodents, do not migrate and instead seek protection elsewhere, such as buildings, caves, or the subnivean zone. The animals that live under the snow will burrow and create more tunnels for living. They will have a nest chamber to rest and birth their young, chambers for storing food, and they have plenty of exit holes used both for entry and exit, but also for air ventilation.

The subnivean zone isn’t without danger. The tunnels can flood or collapse, trapping the inhabitants. Too few air holes can reduce oxygen levels and cause too much carbon dioxide to build up and cause suffocation. They are also not fully protected from predators either. Many predators, such as fox, coyote, and owls, can hear the small animals moving through their tunnels and can make accurate dives into the snow to grab their prey. Smaller predators such as stoats can enter the tunnels and hunt underground. This is where having many escape routes come in handy for the residences of the subnivean zone.

The subnivean zone is invisible from the surface. Luckily, activities such as skiing, and snowshoeing do not harm the subnivean zone. The next time you are exploring a winter wonderland, look for small rodent tracks, they may lead you to an opening to the subnivean zone.

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