The Subnivean Zone, life under the snow: Part 2

Some animals are more active than it appears during long, snowy winters.

This is the second article describing life in the subnivean zone. The first article in the series described the small animals like mice and voles that live under the snow, or in the subnivean zone. This article takes a closer look at the predation of these animals.

The subnivean zone describes a layer in which small animals live under (“sub”) the snow (“nives”; Latin origin). Mice, voles and other small animals live under the snow pack for a variety of reasons. The climate is humid, and the temperature is relatively stable around 32 degrees, buffering the animals from the sometimes blustery wintery conditions above the snow. In addition, food is more readily available under the snow than above it in the form of seeds and delicious bark on stems and roots.

Small mammals also find cover from predators under the snow. This is important because they typically lack winter camouflage and may be seen from long distances when travelling across the stark white snow. Despite being out of sight, these animals are not exempt from predation.

Everyone has to eat – especially in the winter

Predation in the subnivean zone can occur two ways. The first is by predators using the established tunnels to find the small animals; the second is from predators above the snow.

The most common predator under the snow is the “ermine,” or a weasel whose coat becomes white in the winter, usually with a black tip at the end of the tail. Ermine are long and slender, allowing them to burrow into the snow using entrances or ventilation holes to begin the hunt. The ermine follow the tunnels until their meal is found. Ermine may also take over the tunnel and make it their own.

Winter with snow pack can create slim pickings for other predators that do not have the ability to squeeze into the tunnels. Predators such as the fox, coyote, wolf and owls often prey upon the small animals when they travel out of the protected tunnels. The tunnels do not offer unequivocal protection, however, as these predators may also hunt the small animals from on top of the snow.

Fox, coyote, wolves and owls have a keen sense of hearing and can actually hear the activities of the animals moving around in the subnivean zone. The sounds allow them to pinpoint the location of the animals, causing them to jump head long into the snow with the hopes of coming up with a meal. Owls listen from their perches and use their talons to dig into the snow for a meal. And the cycle of life in the forest continues….

Next time you are walking or skiing on the winter snowpack, Michigan State University Extension reminds you to remember to look for clues that animals are actively moving around just below your tracks, in the subnivean zone. 

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