By David Hawke -- Snow insulates, ice not so much. This little fact comes into play in a big way if you happen to be a deer mouse, meadow vole or, occasionally, a ruffed grouse.
These species and others are having a hard time right now, as the recent thaw-freeze cycle we've experienced has left the country side looking more like a glazed skating rink than a cozy white blanket.
Away back in the misty realms of your memories, a grade school teacher probably taught you that animals have three choices to cope with the cold winter months: migrate, hibernate, or adapt. Flash forward to today and yes those “big three” methods are still there, but many nuances have changed the rules for the wildlife that are the players in this game of life. Let's break it down a bit.
First of all, these are not "choices"... a groundhog cannot choose to hibernate one year then choose to migrate the next. A combination of hormones, photoperiod, temperature, and food availability kick-starts the process to either leave, sleep, or change. Each species is genetically programmed to survive winter in its own, sometimes unique, way.
Hibernation is a 'voluntary' process of lowering the body temperature, slowing the breathing, slowing the heart rate, and lowering the metabolism. This complex process takes a long time to get to sleep, and a long time to wake up. Few warm-blooded animals actually hibernate, the local list including groundhogs and meadow jumping mouse. With an empty stomach (because metabolism has all but stopped) and enough body fat these hibernators can sleep for several months.
But what about bears, you may ask -- my teacher always used bears as an example of a hibernating animal. Black bears and grizzly bears do sleep a lot in winter but wake up from time to time, go to the 'bathroom', and even give birth and nurse young. This type of sleep is called a torpor, or light hibernation. Chipmunks do this, as do raccoons and grey squirrels.
Torpor is said to be involuntary, a survival mechanism that is automatically employed if temperatures fall dramatically. Chickadees will do this, as well as migrating bluebirds, clustering together in a cavity until the weather improves.
Migration is a whole other concept, entailing a great physical movement from one area to another. Lack of food, lack of open water, lack of pliable soil, shortened photo period, and lack of warmth will alert hormones to send a message to the brain that will cause wings to flap and feet to move. Birds in general are the best-known migrators, with monarch butterflies coming in a close second on our awareness scale.
Migration is a two-part journey, including going away and coming back. Emigration is just leaving, immigration is just arriving, both being a one-way movement. Migration is the whole round-trip package. (The global crisis of human movement is not 'migration', as it was labeled on a recent CBC documentary... it is more correctly the unexpected immigration and the lack of resources required to house and care for these arriving fellow humans.)
And now adaptation. To adapt or change is an evolutionary option to survive drastic swings in the weather. Thicker fur, new eating habits, a different place to live... these are examples of how some critters change and manage to see the warmth of next year's spring.
Snow is a massive collection of sharp-edged snowflakes; as these jagged snowflakes pile up there are air pockets created in the spaces between the blades. Dead air is a good insulator, keeping what warmth there may be on one side of the blanket, and the very cold air blocked on the other side.
Deer mice and meadow voles are two animals that can survive quite well by living under the snow and above the ground. A cozy nest is made of chewed and woven plant stem fibers, and foraging takes place with daily or nightly forays either digging through the snow or scampering about topside.
Ruffed grouse (also known as partridge) have learned to dive into fluffy snowbanks to sleep a cold night away. The covering snow really does act like a blanket, keeping their body heat trapped within the snowy hollow created by their impact upon landing. This method of survival is not done every night, just when temperatures take that minus-twenty degrees dive.
And so that brings us to today, specifically and generally. Specifically, as the snow has melted away or been rendered into ice, and generally, as our warmer and shorter winters are creating a bit of havoc on the natural world. Without that snow cover, mice are now forced to relocate or at least rebuild their nests. Look for round balls of plant fibers appearing in crotches of trees or within thick stands of shrubs; these are the winter survival homes of these small rodents.
Our natural neighbours are being forced to adapt all their options of winter survival, as the gradual shift of winter conditions from frigid to more temperate conditions is altering the amount of moisture available, increasing the ability to now survive chilly without freezing (a real boon to invading insects), and affecting the triple-timing coordination of spring flowering with insect emersions with bird spring migration. There is a lot going on out there.
We humans have refined the migration sequence for ourselves (think Florida 'snowbirds'), enhanced the adaptation choices with colourful and well insulated clothing including enough snowshoe models to make a snowshoe hare drool with envy, and are working hard to get in the torpor groove... but my caring wife tends to interfere with that last one.
David’s Notebook: When it comes to these frigid cold days, those famous song lyrics come to mind: Should I stay or should I go? Brrr.
Photo: This high-rise mouse nest became a refuge for the residents when the protective ground layer of snow melted away.
© 2019 David J. Hawke