Frozen frogs, a butt-breather and a seasonal genius: How Ontario wildlife survive the winter
CBC’s Great Lakes Climate Change Project is a joint initiative between CBC’s Ontario stations to explore climate change from a provincial lens. Darius Mahdavi, a scientist with a degree in conservation biology and immunology and a minor in environmental biology from the University of Toronto, explains how issues related to climate change affect people across the province and explores solutions, especially in smaller cities and communities.
Surviving a Canadian winter can be a struggle — even with modern heating. But Ontario wildlife have been enduring the cold for thousands of years.
Monarchs and hummingbirds migrate thousands of kilometres, and bats and bears hibernate for months. But there are also animals that survive the winter in your own backyard, in ways you wouldn’t expect.
Here are some of them.
Frozen wood frogs
If you’re fond of winter walks through forests in Ontario — and indeed most of Canada — odds are you’ve tread on a frozen frog.
Meet the wood frog. You’ve probably seen wood frogs in the summer, when they are a common sight across the country.
But when winter rolls around they hide under leaf litter or just a few centimetres underground, where the temperature hovers a few degrees below zero.
And then they freeze.
Their hearts stop pumping, their organs stop working. They don’t breathe and have no detectable brain activity. Their body is encased in ice. You’d think they were dead.
But then comes spring, and they start to thaw — from the inside out.
“They’re alive. Then they get dead during the winter — their life force seems to be going, and then they come back to life,” said Ken Storey, a professor of biochemistry at Carleton University In Ottawa who has done extensive research on the wood frog.
WATCH | Check out this documentary on wood frogs from The Nature of Things:
Freezing every winter seems like an impossible life history — and for most animals it would be.
“Pure water freezes out [of the blood] as ice, leaving behind really concentrated blood, [which] tries to balance itself by sucking the water out of your cells,” Storey said. This starts a cycle where water keeps being pulled out of cells only to freeze, requiring more water to be drawn out.
“Your cells actually die. You die of freezing by shrinking the cells down,” Storey said. Similar to a deflating balloon, if too much water leaves the cell, the membrane starts to collapse inward.
But evolution has given wood frogs a way around this.
It’s all about preparation, Storey said. So wood frogs spend the fall building up energy reserves.
When temperatures drop to freezing, their organs start to shut down while the liver gets to work converting those stores into glucose. As a result, an overwintering wood frog’s blood has 80 times more sugar in it than the average human’s.
“That’s an antifreeze,” Storey said. “You can’t freeze glucose. They have way less ice than you would think at any given temperature because they have so much sugar.”
The sugar lowers the freezing point of the water in the blood and organs, and decreases the amount of water drawn out of the frog’s cells, Storey explained.
As a result, up to 70 per cent of the extracellular water in an overwintering wood frog can freeze without ice forming inside cells, leaving no trace of damage when they thaw in spring.
Ontario is home to eight freshwater turtle species. Six of those species can be found at Point Pelee National Park, including the endangered Blanding’s turtle and spiny softshell turtle, said Julie Charlton, the resource conservation manager at Point Pelee in Essex County in southwestern Ontario.
Ontario’s turtles spend the winter in frozen-over ponds, unable to surface for air, Charlton said.
Instead, they absorb oxygen from the water through several surfaces, including the cloaca — a specialized tissue located under their tails. This process is known as cloacal respiration.
But there’s also a less scientific way to describe it, she added.
“Essentially, in the winter time, they are breathing through their butts.”
The ultimate multi-tool, a turtle’s cloaca has many functions, including excretion, urination, reproduction, egg laying and — in a pinch — oxygen uptake.
Ontario’s adult turtles aren’t freeze-tolerant like a wood frog, and can’t regulate their body temperature like birds or mammals. Instead, they need to find a place to spend the winter where temperatures won’t drop below freezing.
So they hunker down at the bottom of frozen-over ponds and lakes, where the water stays just above zero.
“[Turtles are] ectotherms — I think most folks will say cold blooded — [so they] allow their body temperature to drop to almost zero degrees Celsius while they’re sitting in their cozy little mud spot,” said Charlton.
“Their entire metabolism slows down. They actually decrease their heart rate to one beat every 10 minutes.”
This is known as brumation. It’s essentially the reptile and amphibian equivalent of hibernation, though if you’re lucky, you can still sometimes see turtles swimming around beneath the ice.
Without access to the surface, turtles’ lungs aren’t much use. But they don’t have gills and can’t absorb enough oxygen through their skin like frogs do.
So they get the little oxygen they need through specialized surfaces like their cloaca, which has highly concentrated blood vessels that exchange gases with the water and carry them throughout the turtle.
Since there is less oxygen in a turtle’s blood than in the water, oxygen enters the blood. The reverse is true of carbon dioxide — concentrations are higher in the blood, so it exits into the pond. This passive gas exchange, known as diffusion, happens without the turtle needing to do anything.
So if we’re flexible with terminology, we can indeed say that when turtles take up oxygen through their cloaca, they are breathing through their butts.
Chickadees: Seasonal geniuses
While many birds head south for the winter, the black-capped chickadee braves the Canadian cold.
Common across Ontario, you might not think much of these little birds — but their pea-sized brains might surprise you.
“Chickadees are scatter hoarders. So they store individual food items in dozens of different locations and then they retrieve those,” says Scott MacDougall-Shackleton, a professor of psychology at Western University and director of the Advanced Facility for Avian Research in London, Ont.
“A few hours later, or a few days later or sometimes even longer and they need to use spatial memory to retrieve those stored food items.”
Though they hide and retrieve seeds year round, remembering the location of those stashes is especially important in the winter, when food is scarce. The solution? Make that part of the brain bigger.
“There’s a brain region called the hippocampus, which is critically important for spatial memory,” said MacDougall-Shackleton. “At the time of year when they most need to use their spatial memory is the time that the hippocampus is largest.”
Leading up to winter, the chickadee hippocampus can grow as much as 30 per cent. But that’s not the only way their brain changes throughout the year.
“In the springtime, the regions that control their singing behaviour get new neurons and get larger … almost double in size,” MacDougall-Shackleton said, explaining this likely helps them attract mates during breeding season.
But most birds, including black-capped chickadees, have a number of other adaptations that also help them survive the winter, explained MacDougall-Shackleton.
- Behavioural changes, like huddling together to sleep.
- Seasonal acclimations, like growing extra layers of down feathers.
- Evolutionary adaptations, like regulated hypothermia and a specially adapted circulatory system.
This circulatory system, known as countercurrent heat exchange, involves pairing arteries carrying warm blood from the animal’s core with veins carrying cold blood from the extremities, especially the feet. This way, the heat transfers into the blood heading back to the heart and less heat is lost to the environment.
This has independently evolved in many animals, including mammals like coyotes and wolves. In fact, all of the adaptations discussed here evolved multiple times, sometimes in very different species — a process known as convergent evolution.
After all, there are many ways to survive a Canadian winter, many more than we’ve covered here. But when something works well, evolution tends to bring many species to that same solution.
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