Under The Ground, Under Water: How Frogs And Toads Spend The Winter.
October 25, 2021
When the bracing autumn days cool and a thin layer of snow occasionally whitens the landscape, we know winter is at hand. The countless songbirds of our forests flee the cold of our winters and the lack of food by migrating south.
Other animals are adapted to the cold and may develop thicker fur or feathers. Some have the ability, enviable in our view, to be able to sleep throughout Ontario’s long winter, that is, to hibernate.
What Is Hibernation?
To hibernate, the animal lowers its metabolism to the point of using very little energy; even his heart rate and body temperature drop, and normally he does not eat. Many animals do this: from bears to jumping mice, and also turtles and snakes, and even many insects overwinter in hibernation.
Cold blooded animals (which cannot produce their own body heat using their metabolism) such as reptiles and amphibians must hibernate in Ontario; it’s far too cold to stay active – they would freeze and die. To survive this tough season, they just need to find the right place.
For most frogs, the right place is underwater. We often think that the water is very cold in winter. But, as the freezer ice bucket shows us, the water is liquid until it freezes. If the water is still liquid, it is above freezing – but barely!
Many of Ontario’s frogs, such as the bullfrog, green frog, northern frog, and marsh frog, hibernate in water. Many believe that these frogs burrow into peaty soil at the bottom of a pond or river to “keep warm” and stay hidden from predators.
But it turns out that – in order to survive the winter under the ice – they have to stay out of the mud because …
These frogs breathe through the skin!
Very cold water (4 ° C) contains more oxygen than hot water, which is good for frogs. They can simply absorb the little oxygen they need directly from the water through their permeable skin.
If they were buried in mud, their oxygen reserves would quickly be depleted. This is why they remain exposed to the bottom, or perhaps nestled among stones, logs or roots – to be constantly supplied with oxygen by the movement of the water.
Toads commonly found on trails and in gardens, such as the American toad, hibernate on land. As forests and fields freeze, of course, and even the ground freezes, toads must find a place that is safe from freezing.
For that, they dig! The rear feet of toads have a hardened outgrowth that allows them to dig into the ground. They must dig, often more than 50 cm, to the depth of frost, where they will overwinter.
It is only after the temperature of the soil has warmed in the spring that they will emerge.
Frozen Frog Lollipops?
A few other frogs deal with the cold a little differently – they’ve found a way to become the cold themselves! Our wood frog and the three species of tree frogs found in Ontario (gray tree frog, cruciferous tree frog, and chorus frog) are actually frost tolerant.
Before you bring up visions of frog lollipops, remember this: These frogs don’t freeze like, say, a hot dog. These tree frogs and wood frogs hibernate in leaf litter, or under bark – places that are not really insulated from the cold.
When the temperature drops below -5 ° C, tiny ice crystals form in the body, freezing about 40% of its water content.
Then the frog stops breathing, its blood circulating and its heart beating – you might think it is dead. When spring arrives, the frog thaws – sometimes in a single day – and it can then resume its activities.
Other animals cannot freeze and withstand winter this way: Ice crystals can severely damage their cells, causing death.
So the next time you see a frog in the spring, you’ll know it must have survived harsh conditions the previous winter – that’s enough croaking!