Nature News from GYE #23

March 7, 2021

Snug in the Snow…
Have you ever been outside on a winter day and wondered what the warmest place to shelter might be if a sudden storm came up? Snow shelters have been used through millennia in cold climates, so the idea of building an igloo or snow cave is not new, but wild animals use snow as a shelter as well. Layers that form as the snow pack increases can be a matter of life and death for critters that tunnel into air spaces that form as this snow crystalizes. Fresh snow traps airspaces and as it accumulates the moisture and temperature will determine how the snow bonds or breaks down to form new crystals. Lower layers of snow age through the winter and eventually form either a stable bonded base or more fragile, full of air pockets, base. The air in these layers stays a constant temperature which is close to 32 degrees F; much warmer than many of the coldest nights. O2 levels stay consistent as a CO2 exchange continues. The smallest of creatures; voles, mice, shrews and some insects, can survive in these dark layers below the snow and close to the ground.

Subnivean Zone from

This habitat is referred to as the subnivean environment. Squirrels and birds have cached sees and nuts at the base of trees. Seeds from grasses and shrubs, dry berries, bark from the shrubs and insects are all found at the ground level where the temperature is consistent. Some small critters will generate heat by subtle shivering. Some birds, like Grouse, will plunge into a snowy pocket for the cold night and stay warm as though they were in the warmest sleeing bag. Evidence of all of this can be seen on the surface of the snow with the tracks and other sign left with the struggle of survival

Clark’s nutcracker ( that cache seeds for winter food at the base of trees) in snowfall near Silver Gate, MT; Jim Peaco;
Red squirrels also cache cones as a Winter food source
Grouse plunge into the snow for the evening
Photo by Dan Hartman

Under the snow, these smaller creatures are hidden from predators. Living under the snow is not without risk. Owls can hear mice and voles running around underground from great distances. They also have night vision super powers with the number of rods in the back of their eyes that allows them to see much more clearly in the dark. Owls detect these subnivean lives and can plunge into layers of snow to grab their prey. Foxes and coyotes detect by scent as well as sound.. With an acrobatic pounce, these predators will dive right in for their meal. Another potential hazard can occur if a tunnel collapses, which can cause suffocation.

Some animals that have darker fur will molt in the fall and by the time snow is covering the ground, they will have a white fur coat that camouflages these critters. Examples of this are the different species of weasel that turn white in winter ( then called Ermine) except their black nose and black tipped tail or the Snowshoe Hare which have the same cryptic coloring in the winter months.

Weasel on the left and in it’s winter coat, an Ermine
Acrobatic pounce of a Red Fox, Zack Baker
Other animals such as Black Bears and Grizzly Bears will hibernate in dens they secure in the fall months. The cubs are born in the dens

Many other adaptations occur in winter as well. Birds fluff up their feathers to increase the insulating layer and at times will tuck their heads into their feathers to decrease heat loss from breathing. Otters, muskrats and beaver have dense underfur that traps air to keep cold water from contacting their skin.

Pikas (the smallest animal in the Rabbit family) do not hibernate so they are storing vegetation all summer between rocks in boulder fields and talus slopes (their pantries) for their winter food source. They survive in these air pockets between the rocks and are seldom seen on top of the snow as they are avoiding predators!

Pika gathering food for it’s winter stash, Dan Hartman
Elk and other mammals in Yellowstone can be seen in thermal areas where warm ground keeps snow from accumulating at depth.

One last physiological adaptation to winter is a heat exchange circulatory system that occurs in waterbirds and even some mammals that allows them to stand on ice or cold water. This is called “counter current heat exchange”. The heat from warm arterial blood warms venous blood that is returning to heart. Now that is an adaptation!

American Dipper in winter, Sacajawea Audubon

Wild lives in northern latitudes have only a few choices as winter approaches. They either hibernate, like the bears, marmots and ground squirrels or they adapt in many ways I have shown you above. One last option is what so many birds and butterflies do. That is migrate either hundreds of miles to warmer climes, or at least to lower elevations with less snow and more food availability. It’s all about food, shelter and water and the instincts shown in the natural world are remarkable.

We are in a warming spell right now and snow pack is consolidating and shrinking. As March continues, we will typically have a few more big snowfalls and cold weather ahead of us. Not time to put away the snow shovels yet!

Wishing you all the joy and beauty of these changing seasons, Leslie

Fox’s Garden by Princesse Camcam

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