Staying alive through the winter
Winter is on its way to BC – the Lower Mainland is not usually very cold, but the rest of BC can be ver-r-r-y cold indeed. So how do living things keep on living through the cold?
We humans have lots of ways to keep warm during winter – warm homes, warm clothes, warm food: our neighbours in nature are often not so lucky and have found different ways to survive.
Many birds migrate – they just wing off south to warmer climates until winter up here is over, then they come back to lay eggs and raise their young. Other birds like chickadees, jays and nuthatches stay around and store food to feed themselves through the winter. These caches of seeds and nuts may be stored in more than a hundred places but with their amazing powers of memory, the birds can remember where all of them are. With any luck, there will be enough stored food for the whole winter. For many species, one of the most common ways to survive is to sleep the winter away.
Deciduous trees shed their leaves. Why? In winter, water freezes to ice and as a tree can’t absorb ice, it can’t maintain its water balance. The sap inside leaves might freeze which would kill them and perhaps the tree as well. The tree needs to save heat and water and as it can live without its leaves for a while, it drops them and shuts itself down into a dormant state. It just ‘sleeps’ through the winter. Evergreens like holly and conifers don’t shut down; they have a waxy coat on their leaves or needles to protect them. The roots of conifers can continue to take up water – the ground under snow often is not completely frozen.
When animals sleep the winter away it is called hibernation.
Marmots and Chipmunks
Marmots hibernate for seven months, more time than they are awake! Living only on stored body fat, Yellow-bellied and Vancouver Island marmots hibernate in deep burrows, some as much as five metres long. The burrows of Hoary marmots are often under a large boulder which protects them from being dug up by hungry Grizzly Bears. Chipmunks hibernate in cozy nests inside a hole in an old tree. Here they have stored nuts, berries, seeds, fruit, and grain; they can nibble on these any time they wake up and feel hungry.
Frogs, Toads and Turtles
Many frogs and turtles brumate – they spend the winter buried in mud in the bottom of deep lakes far below the ice. All their body functions slow down and they do not breathe – they can absorb enough oxygen through their skin. Toads, however, prefer to hibernate on land. They hide in many places such as river banks or ground squirrels’ burrows – even if the squirrels are still in there!
Garter snakes hibernate in a den below the frost line for up to sixteen weeks. This den is called a hibernaculum and they use the same place year after year. Hundreds of snakes gather together in one hibernaculum, keeping each other warm. To see these hundreds of snakes emerging from the hibernaculum in spring is an amazing sight.
With any luck, bears will have had good foraging during summer and fall so they have lots of body fat to last the winter. They make dens in caves, hollow trees and big cracks in rocks and bring in some leaves and twigs to form a nest; they get settled in around October or November depending on the weather and wake up again in the spring. During all that time they will not eat or drink; they live on their body fat. In January, a pregnant black bear will wake up long enough to give birth in the den to one or more cubs. She then goes back to sleep, waking now and then to lick the cubs and give them some attention. Cuddled against her body the cubs do not sleep, they suckle their mother. When they are about three months old, mother bear wakes up and takes them out into the world.
Would you like to sleep the winter away? I doubt it – you’d miss a lot of school which might please some, but you would also miss Halloween and Christmas, snowballs and sledding and movie specials and ——— ! I think you would rather stay awake!
This story appeared in NatureWILD, volume 13, issue 3 from 2012.
Image credit: J. Pelletier (www.hww.ca)