The Secret to Turtle Hibernation: Butt-Breathing

Breathing or not breathing, that's the question.
What would happen if you were submerged in a pond where the temperature of the water floated just above the freezing point and the surface was covered by an ice cap for 100 days?
Well, obviously you would die.

Butt-Breathing Turtles? Yes, That’s a Thing

Turtles are the unlikely champions of getting by without oxygen. As Smithsonian ornithologist George Angehr related to The Straight Dope, turtles can survive for more than a day in a chamber containing nothing but nitrogen gas. Sometimes, however, even a turtle gets a little winded. What do they do when they’re hiding underwater and they need some fresh air?
Some turtles, such as the eastern painted turtle of North America, have come up with a unique solution. They can breathe water through their rear ends.

This bizarre-seeming adaptation is actually very clever. Turtles have inflexible shells, so they can’t breathe by expanding their chests the way most animals can. In fact, breathing takes a bit of elbow grease and some workarounds when you’re a turtle. By breathing through both their front and rear ends, they can take in oxygen without expending as much effort.
The white-throated snapping turtle of Australia is another species that shares its American cousin’s methods. Both species have rearward sacs that open out into the cloaca, a versatile orifice located under the tail. While we have a similar orifice, the anus, which we use for excreting waste, reptiles use their cloacas for peeing, pooping, and laying eggs. These turtles add breathing to the already long list. The sacs pump water in and out of the cloaca, picking up oxygen along the way.
The scientific name for this process is cloacal respiration, and some fish can do it, too. Not only is it more efficient to breathe through both ends, cloacal respiration also allows turtles to stay underwater for longer. These turtles can hide for predators for up to days at a time by breathing through their butts. Some can even bury themselves in mud and hibernate for up to five months while slowly breathing via their cloacal sacs.

Unfortunately, despite this neat trick, turtles are in trouble. Like a lot of animals that live in the water, pollution and the fishing industry have hit them hard. Scientific American reports that, as of 2014, the white-throated snapping turtle is critically endangered. It needs clean water to pull off cloacal breathing. As the water it lives in becomes polluted, cloacal respiration becomes more difficult, and the turtles need to surface more frequently to get enough oxygen. Surfacing exposes turtles to dangerous predators.
One way to help save turtles around the world is by donating to wildlife organizations. If you want to help turtles like the painted turtle and the white-throated snapping turtle survive, visit the Rainforest Site and donating to campaigns such as the effort to save hawksbill turtles from deadly nets.
And that's because you're not as cool as a turtle. And by great not only I mean incredible, I mean literally great, like cold. Also, you can not breathe through your ass.
But turtles can, which is just one of the many reasons why turtles are truly amazing.
Cold weather slows down
As an ectotherm, an animal that depends on an external source of heat, the body temperature of a turtle tracks that of its environment. If the pond water is 1 ℃, so is the body of the turtle.
But turtles have lungs and breathe air. So how is it possible that they survive in a frozen pond with an ice cap that prevents them from getting into the air? The answer lies in the relationship between body temperature and metabolism.
A cold turtle in cold water has a slow metabolism. The colder it gets, the slower your metabolism, which translates into a lower demand for energy and oxygen.
When turtles hibernate, they depend on stored energy and absorb oxygen from pond water by moving it through the surfaces of the body that are flush with the blood vessels. In this way, they can get enough oxygen for their minimal needs without using their lungs. Turtles have an area that is especially well vascularized: their butts.

Look, I was not kidding, the turtles can really breathe through their butts. (The technical term is cloacal breathing)
Not frozen, just cold
We are not turtles We are endotherms (expensive ovens of metabolic heat) that need to constantly feed our bodies with food to generate body heat and maintain a constant temperature to stay alive.
When it's cold, we pile on our clothes to trap the metabolic heat and stay warm. We could never get enough oxygen in our vascularized surfaces, apart from our lungs, to supply the high demand of our metabolic kilns.

For humans, a change in body temperature is a sign of illness, that something is wrong. When a turtle's body temperature changes, it's simply because the environment has become warmer or colder.
But even ectotherms have their limits. With very few exceptions (for example, box turtles), adult turtles can not survive sub-zero temperatures; They can not survive by having ice crystals in their bodies. This is the reason why freshwater turtles hibernate in water, where the temperature of their body remains relatively stable and does not drop below zero.
The water acts as a temperature absorber; It has a high specific heat, which means that a lot of energy is needed to change the water temperature. The water temperatures of the pond remain fairly stable during the winter and an ectotherm sitting in that water will have a similarly stable body temperature. The air, on the other hand, has a specific low heat, so its temperature fluctuates and becomes too cold for the survival of the turtles.
Calamitous muscles
An ice-covered pond presents two problems for turtles: they can not emerge to breathe, and little new oxygen enters the water. In addition to that, there are other creatures in the pond that consume the oxygen produced by aquatic plants during the summer.
During the winter, as the oxygen is spent, the pond becomes hypoxic (low oxygen content) or anoxic (no oxygen). Some turtles can handle water with low oxygen content, others do not.
Snapping turtles and painted turtles tolerate this stressful situation by changing their metabolism to one that does not require oxygen. This ability is surprising, but it can be dangerous, even lethal, if it lasts too long, because acids accumulate in your tissues as a result of this metabolic change.
But, how much time is "too long"? Both snapping turtles and painted turtles can survive forced submersion at cold water temperatures in the laboratory for more than 100 days. Painted turtles are the kings of tolerance to anoxia. They mobilize calcium from their shells to neutralize the acid, in the same way that we take antacids that contain calcium for heartburn.
In the spring, when anaerobic turtles emerge from hibernation, they are basically a major muscle cramp. It's like when you make a difficult career: your body changes to anaerobic metabolism, lactic acid builds up and gives you a cramp. Turtles are desperate for sunbathing to increase their body temperature, to activate their metabolism and eliminate these acid byproducts.
And it's hard to move when they have that type of cramping, making them vulnerable to predators and other dangers. The spring emergency can be a dangerous time for these lethargic turtles.
Tracking turtles in cold weather
Field biologists tend to investigate during spring and summer, when animals are most active. But in Ontario, where winters are long, many species of turtles remain inactive for half their lives.

Understanding what they do and need during the winter is essential for their conservation and habitat protection, especially since two thirds of the turtle species are at risk of extinction.
My research group has monitored several species of freshwater turtles during their hibernation. We attach tiny devices to the turtle shells that measure temperature and allow us to follow them under the ice.
We have discovered that all species choose to hibernate in places of wetlands that float just above the freezing point, that move under the ice, hibernate in groups and return to the same places winter after winter.
Despite all this work, we still know very little about this part of turtle life.
Therefore, I do what any committed biologist would do: I send my students to do field research at -25 ℃. We are not restricted to the biology of good weather here.
In addition, there is an incomparable beauty in a Canadian winter landscape, especially when you imagine all those incredible turtles under the ice, breathing for their butts.
Jacqueline Litzgus, Professor, Department of Biology, Laurentian University
This article was originally published in The Conversation