How Animals Cope in Winter

Featured above is the Pine Martin. Photo by Jennifer Howard

By Elizabeth Trickey

How often have you looked outside on a cold, blustery, winter day and seen a squirrel poking around in the snow bank, looking for that lone peanut under the tree that it stashed away in the autumn?  I’ll bet you felt sorry for the little critter.  Wanted to pick it up and bring it into your house to warm up by the fire.  Well, no need for that! 

Nature has provided animals with many different ways to cope in the winter.  Some migrate to warmer climates, some hibernate, some go into torpor, and most develop resistance tolerance strategies.  And it’s not just the cold in winter that requires changes in the animals’ behaviours.  The days are much shorter so there is not as much sun to warm a body and not enough daylight for diurnal animals to look for food, trees and bushes have lost their fruit, the ground may be covered in deep snow where food sources are located, the soil is so frozen that’s it’s difficult to dig for insects or tubers, water sources freeze over, and the white snow creates a bold contrast to the fur of animals that are trying to escape predators.

Nature does have a plan for all of that, making sure that every species is able to get what it needs to survive.  The one thing that is common to most animals as winter sets in, is that they eat lots.  Whether migrating or sticking around, they fatten up while they can.  They instinctually know that there will be lean times ahead.

Now where should I begin.  Aaahhh, I know – with all the animals that can’t stand the heat, so get out of the kitchen.  Mmmm.  Bit backwards.  They can’t stand the cold, so they get out of the freezer.  Now that’s better!  The animals that live furthest north are the ones that begin their migration earliest.  Some of these critters have very long journeys ahead of them, some of which take months, so they need to make sure that they leave in enough time to get to their destinations.                                                                                                                                                                                                                                                                

 

Caribou Migration by WWF-Canada

Migration is not without risks, and these risks are getting more severe due to habitat destruction, new builds such as wind turbines, and climate change.  Imagine heading off to your cottage for the summer to find it gone, a shopping mall in its place!  Or the cottage is still there, but the lake has all dried up!  Not a pleasant surprise for you, and certainly not one for the animals who were counting on having a place to go. 

In the effort of migration, animals have to contend with bad weather, the possibility of getting lost, and predators that know the migratory routes and are lying in wait for dinner.  But all these risks are peanuts compared to staying in a freezing environment that offers no food source, and that the animals are not physically capable of enduring.

Animals that migrate do so for several reasons.  For many it is due to the cold temperatures, sometimes it is to find more abundant supplies of food and water, and other times it is for breeding purposes.  The animals ready themselves for the big trip, partly through instinct, partly through being taught, and partly by being aware of the clues in their environment such as the Earth’s magnetic field, the moon, stars, wind patterns, smells, and group communications. 

Migration is movement from one area to another.  It doesn’t mean that every species goes the same distance south, or for that matter, even heads south.  Warmer temperatures are also found on the west coast. Earthworms migrate by wiggling further underground, below the frost line.  Some animals that migrate include Canadian Geese, certain types of bats, caribou, spotted frogs, deer, moose, elk, grey whales, dragonflies, bighorn sheep, monarch butterflies, and hummingbirds.  And, of course, an older generation of the species Homo sapiens, more commonly known as “snowbirds”.

So now let’s look at the species that don’t migrate, though are rarely seen, if ever, through the coldest parts of the winter.  Where are they, what are they doing, and how do they actually survive?  Good questions!  Answer?  Well, that’s something researchers are still learning about.  As technology improves, we become more adept at spying on these animals in their dens, and we are able to learn more about altered states.  It is extremely important, though, that these animals are not disturbed during this research, not because they’d be mighty ticked off at us for interrupting their quiet time, but because the energy they would expend by dealing with any disruption could be fatal for them.

At this point, scientists have looked at 2 altered states, one being hibernation and the other being torpor.  The animals that go into these states are not just sleeping.  Their bodies go through amazing physical changes that allow them to preserve energy since they will be eating very little, or nothing at all, over many months. 

For several reasons there is confusion as to which animals go into hibernation and which ones go into torpor.  Not all animals of the same species live within the same weather zones.  Black bears in northern Ontario experience a very different winter than the black bears in western Canada or the southern USA, so their circumstances are different.  As well, the issue of global warming has changed weather patterns, which greatly influences the way animals deal with the winter months. 

Torpor and hibernation are very similar survival tactics whereby metabolism, heart rate, and breathing all slow down, and the body temperature drops significantly.  Torpor might be described as the initial state that denning animals go into during the cold months.  They are still able to occasionally eat from stored food sources within their dens, or even move outside if there is a period of mild weather.  Hibernation is like a prolonged, deeper, type of torpor.  The animals in this state usually do not eat at all and many do not even produce waste products.

Winter-resting animals, whether going into hibernation or torpor, often fatten up before the big winter shutdown because they don’t anticipate getting up to eat for a while so they need the excess body fat.  Some of the torpid animals that wake from their rest every couple of days/weeks, to eat and do their business, don’t always bulk up in the fall.  Instead, they will hoard food in their dens so as to always have something to eat nearby.

One might wonder why black/brown bears have to hunker down for the winter when their cousins, the polar bears, need, and thrive in, the freezing temperatures.  Well, they tuck away for the winter, not because of the cold, but because there isn’t enough food available that they usually consume.  That’s the same for bats that feed on insects or groundhogs that feed on vegetation.  If they didn’t go into hibernation or torpor mode, they would starve to death. 

Animals that go through these cold-weather resting periods need to find or build themselves a nesting area where they won’t be disturbed by predators. Their winter homes are referred to as “hibernacula”. 

Bears bed down for the winter in tree hollows, felled trees, or caves.  They do not eat, urinate or defecate during this time.  Instead, their bodies feed off the excess fat and then recycle the wastes, turning the urine into a protein, which is used to maintain muscle mass and organ tissues.  During this time, pregnant females will give birth to her cubs.

 

Little Brown Bats, hang out (literally!) in caves, mines, attics, or rock crevices.  They choose these roosts since they provide the high humidity which bats need, as well as a consistent, cool temperature that never goes below freezing.  They fatten up with insects during the summer and fall because they do not eat at all during the cold months.  However, they do occasionally wake to drink and eliminate wastes.  Many, but not all, bats spend their winters in a large group, cuddled up. 

Groundhogs enjoy a very long, deep sleep, so really pack on the groceries before burrowing down for the winter.  Some stay in their same tunnel while others retreat to hibernacula in the forest, which provide more safety from predators.  Older groundhogs are the first to bed down, while the younger ones take more time to fatten up. Their body temperature lowers to 3°C, their hearts beat only 4-5 times per minute from the usual 80 times, and the usual 16 breaths per minute are cut down to only 2.  Groundhogs need to get in a good rest over the winter so they will be ready to predict the coming of spring on February 2^nd!

Some critters that we don’t usually see during the colder temperatures do not fatten up, even though their regular food may be difficult to find in winter.  Instead, they hide food around their habitat or build up stores within their hibernacula that they will need throughout the winter.  Because they might rarely be leaving their homes to find food, they will block the entrances from predators and make sure they have everything they need to survive inside. 

Chipmunks are an excellent example of an animal that hoards food.  Nature has provided them with those expandable cheeks, which they cram full of nuts and seeds to take back to their burrows in the ground, for when it gets too cold to go outside to forage.  Their tunnels have an area for sleeping and another for food storage, though some chipmunks will keep their stored food under their nests for easy access.  If there is a mild spell in the winter, they might even come out of hiding for some fresh air and to entertain us with their antics!

Many animals in Ontario make sure they have plenty of additional fat and fur to see themselves through the winter, such as raccoons, skunks, and squirrels.  These critters will often share their homes with others when denning down for the winter.  They spend a lot of inactive time during the coldest periods in order to conserve energy, but their metabolism is not altered as with animals that are torpid.  They tend to be seen out of their dens, foraging for food, on the more mild winter days.

 

Then there are the tougher animals that are out and about for most of the winter.  They are more physically able to withstand the colder temperatures and they are able to satisfy their dietary needs within the habitat.   Many of our all-weather friends adapt to the winter weather by growing thicker fur, sort of like when we a start wearing hats, mitts, and a heavy coat to go outside in the winter!  Some animals, like the Arctic Fox or Snowshoe Hare have their fur change to a lighter colour for camouflage in the snow.

 

 

 

 

 

 

 

Polar bears are very active in the winter since this is the time when they can travel out on the ice to find their prey, the ringed seal.  Their fur colour blends in well with the snow and ice, giving them camouflage from the seals that they hunt. 

Rodents, such as the muskrat, porcupine, and beaver, have active lives in the winter.  Beavers create dams that keep deeper water open throughout the winter.  This allows them to transport and store large food items like tree trunks and branches, underwater, at the entrance to their lodge.  When preparing dinner for the family, all the chef has to do is swim out to the cache of branches and bring it into the lodge!  The open water also provides an underwater escape from predators that might get into the lodge through above-ground tunnels. 

Muskrats enjoy similar winters as beavers, only they do not usually store food.  They must forage in the wild, mostly underwater, on a daily basis.  Their thick fur is waterproof, and to help keep warm in winter, they tend to live in small groups.

Porcupines have 2 types of fur to keep them warm in the cold weather – a soft, woolly undercoat and longer guard hair.  Although solitary animals, they will team up with other porcupines when denning in the winter. Porcupines are very slow moving rodents with short legs.  Undaunted, they will struggle through snow banks as they forage for food, leaving paths like little snow plows, clearing a route to the feeding areas.  They will use these paths until the next snowfall, and then they have to start plowing again.  Moving through deep snow takes a lot of energy, which can have adverse effects on the porcupines’ chances of surviving the winter. 

Rabbits, another hearty winter animal, have some interesting adaptations to help them survive in the winter.  Apart from the usual extra fur growth, reduced activity, cohabitating with friends, and eating extra food to build up fat stores, they look for different types of food to eat.  Their regular summer meals consist of berries and green vegetation.  In winter, this it changed to a more wood-based diet such as twigs, buds, and tree bark.  They also start eating more of their own faeces, which still contains important nutrients, especially Vitamin B.

So many critters are active in the winter and they all have their special ways of coping with the cold and potential lack food.  Nature makes sure that all animals are prepared for each season, that they have the means to withstand the cold, and that there is food available for them.  It truly is awesome. 

Speaking of which, did you know that this week there is another special day observed?  There sure is!  It is the International Day of Awesomeness!  So on Wednesday, March 10^th, let’s all celebrate our wild friends, which are unique and awesome all through the year!

 

Winter photos below are courtesy of Debra Spilar and Jennifer Howard.