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Ever wish you had your own secret network of hidden passages? Well some animals do and they might be closer than you think!

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Jessi: Squeaks and I were just exploring out in the snow, and we found something amazing.  Right in the middle of the snow, there was a small hole, too small for either of us to fit into.  That hole in the snow led down to a small dark tunnel.  It did look just like a secret entrance to a snow fort, Squeaks.  As we kept looking around, we found more and more of these holes until we found someone popping out of one of the tunnels.  It was a vole, a small rodent just like Squeaks that lives in meadows and fields.  As soon as he noticed us watching him, he turned right back around and scurried down into his tunnel.  After a few more minutes, he popped back up from another entrance.

You're right, Squeaks, those tunnels are connected deep under the snow.  The vole has been working on his tunnel system since the snow first began to fall.  It leads to a special space under the snow but above the ground called the subnivean zone.  'Sub' mean 'under' and 'nivean' means 'covered with snow', so 'subnivean' just means 'below the snow.'  

That's right.  Even though it might seem like the layer of snow on the ground is hard and packed down, there's actually some space under there where there isn't much snow.  The empty space forms because when snow falls outside, some of the snow doesn't make it all the way to the ground.  Some of the snow gets stuck on the stems and leaves of sturdy plants, tree trunks and roots, and even rocks.  As more snow gets added, the plants and rocks act like tiny umbrellas, leaving a special gap where the snow can't reach.

Eventually, it looks like a tiny pocket of air hidden completely under the snow, with a leaf or a stem for a roof.  In an area with lots of sturdy plants, like a big meadow, lots of small pockets can form and connect to each other, creating a secret space under the snow that's perfect for little creatures like voles.  These animals will dig tunnels down to the subnivean zone and use it as a special shelter during the winter, only coming back up above the snow when they really need to.  

I know, it does sound like it should be pretty cold under all that snow, but it's actually surprisingly warm.  The subnivean zone is protected by the layer of snow above it, so even if a cold wind is blowing above the snow, the subnivean zone stays just above freezing.  So that special space under the snow is a perfect warm shelter for our little vole friends.

Small animals like the vole can also use this subnivean zone to stay safe from predators that might want to eat them.  Lots of predators like foxes search for their food by looking around with their eyes, then hunting down the prey animals that they see, but if prey animals like the vole are under the snow, predators can't see them.  Most predators are too big to fit into the subnivean zone, so prey animals are pretty safe if they stay below the snow, as long as they stay very quiet, but foxes also have great ears, and they know to listen for scurrying sounds under the snow.  If they hear prey, they'll jump right through the snow and try to reach the animals hiding in the subnivean zone.

Don't worry, even if the fox tries to get him, that vole has lots of tunnels that he can escape to.  Lots of animals have many different rooms and tunnels in their subnivean shelters, including places for sleeping, storing food, eating, and even back up tunnels for getting away from any predators.  The subnivean zone is like an entire world made out of snowy tunnels.  Even though we can't see it from the surface, there's so much to explore down there.

Have you ever found tunnels outside that animals might use?  What would your subnivean shelter look like if you were a vole?  Ask a grown-up to help you leave a comment down below or send us an e-mail to  Thanks and we'll see you next time here at the Fort.