By Katrina Bellefeuille
Animals that build their homes in the subnivean zone
During Canada’s long winter months, it is common for many of us to find sanctuary in our homes especially after a chilly day exploring the outdoors. Typically, we will throw on some cozy pyjamas, drink hot cocoa and wrap ourselves in a plush blanket.
What if we told you that some small mammals actually use the snow to stay warm? The snow might seem like the opposite of cozy and warm, but to these little critters the snow is absolutely crucial to their winter survival. Let’s dive into the subnivean zone!
What the Heck is the Subnivean Zone?
Between the ground’s surface and the bottom of the deep snowpack, tiny mammals carefully craft tunnel systems that help them navigate the zone in the winter. This special area is where these mammals seek protection from cold temperatures and hungry predators.
The rising warmth of the ground and organic debris physically supporting the snow forms the subnivean zone. Don’t get us wrong; the subnivean zone is not exactly “toasty warm”. The average temperature rests at around 0°C, but can still dip below that. However, the snow provides critical insulation that makes it a whole lot better to tolerate than surface temperatures.
Residents of the Zone
We know what you might be thinking - who would be wild enough to live under the snow in the middle of February? Some of our animal friends that reside beneath the snow include rodents like mice and voles. Mole-like mammals called shrews also spend their winters in the zone.
Unlike many animals such as bears that hibernate in the winter, these mammals are active throughout the season. The tunnels they work hard to construct act as a connection between food and sleeping areas. Ventilation shafts at the surface release excess carbon dioxide formed from their breath.
What’s for Dinner?
Subnivean zone-dwellers have access to a top-secret food buffet untouched by frost and bitter winds.
Shrews, the insectivores of the group, have an impressive metabolism. Like teenagers, they’re always hungry, often eating the equivalent of their body weight in food every day if accessible. Their meal of choice consists of insect eggs, larvae, pupae, dormant adult insects or dead animals. Mm, tasty!
Voles are omnivores and live in an underground tunnel system year-round. Leading up to the winter, they are busy creating burrows to stockpile food such as bark, roots, lichens, funghi and insects, ensuring that they have enough to eat until spring.
Then there are mice, the vegetarians of the group, which also have a hefty appetite. Mice enjoy munching away on things like leaves, berries and other grains.
Life in the subnivean zone can still be risky. Although they cannot see what is beneath the snow, predators like coyotes, owls and foxes have a powerful sense of smell and hearing. This makes it easier for them to hear the faint pitter-patter below them and sometimes trap their prey by forcefully pouncing into or digging up the snow. The slender weasel, another common predator, hunts by squeezing its way into the tunnels!
Should there be an early rainfall or quick thaw early spring, the subnivean zone can sometimes be flooded or collapsed on by the snow. However, this doesn’t seem to affect its dwellers’ survival rates as seen by their consistent cyclical population numbers. When the weather begins to warm up, they can easily use the ventilation shafts as an escape hatch to vacate the premises.
Wildlife clearly have a fascinating toolkit of survival techniques that help them face many challenging conditions. Perhaps next time you look out your window while enjoying your hot cocoa, you can imagine all of the tiny mammals that have found their very own sanctuary just below the sparkling snow in the subnivean zone.