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'Butt breathing' is turtles' secret to survival

2021 10 03 hawke turtlesBy David J. Hawke -- While stepping with great care and caution into the canoe (I have to reluctantly admit that I’m not as agile as I used to be) my enthusiasm for the adventure ahead had to be held in check and focused on the task at hand. Getting a soaker, or worse, before even leaving the shore puts a real damper on the day. (Get it? Soaker… damper?)

It was indeed a perfect almost last day of summer: warm air, light breeze, bright sun. And the river on which I was paddling was devoid of the usual droning of summer watercraft; for this moment it was just me, my camera, a canoe and a drifting current. Seize the moment, as they say.

As the current carried me along, the shoreline wildlife basically ignored me. Great blue herons stalked the shallow waters, families of wood ducks dabbled about in the duckweed covered bays, and turtles basked on every log that was big enough for them to climb on to.

The turtles in this case were Midland painted turtles, and they were reluctant to drop back into the water even as I drifted by in close proximity. They were obviously trying to soak in as much solar energy as possible and given that it was a rare sunny day, an interfering canoeist was tolerated more so than perhaps on a hot day in August.

Turtles are in a group of animals that are called “ectothermic,” so this last blast of warmth is critical to their winter preparations. “Ecto” means outside and “thermic” is body temperature… the old term most of us were brought up on was “cold blooded”. To balance the explanation, “endo” means within, so an endothermic creature (such as a human) has its body temperature regulated from within, by the burning of sugars and the mixing of oxygen in the blood.

A warm day makes for a warm turtle. But the coming days will rapidly be getting less warm, so what’s a turtle to do? Migration is out of the question, and adaptation is a tough sell to a turtle, so they will be practising the discipline of hibernation.

To hibernate, to go into a deep prolonged sleep, usually requires a lot of autumn preparation. Mammals that hibernate, like ground hogs and jumping mice, eat oodles of food just prior to bed time and rely on the fat reserves of the body to replenish the energy needed for survival. Not so with turtles.

A hibernating mammal, despite an incredibly low rate of respiration, still has some surrounding air is available to them. But turtles spend the winter months buried in mud at the bottom of the pond, with no way to break through the ice above to grab a fresh breath. So how do they do it?

The heartbeat of a turtle drops from 40 beats a minute in the summer to one beat every 10 minutes while hibernating, so the need for abundant oxygen to mix with the blood is much reduced. But still, oxygen is required, considering the turtle will be underwater for four to five months. How do they do this? Butt breathing!

While our rear end is often used to expel gas (oh, come on, you do so!) a turtle’s rear becomes the place where oxygen is extracted from the water via a highly vascularized skin membrane and is taken into their body. Their throat skin also is capable of absorbing oxygen from the surrounding water.

Remember that water does not freeze all the way to the bottom of a pond; only the upper layer that is exposed to subzero temperatures will condense into ice. The unfrozen water below is still darn chilly (about plus four degrees) but remains liquid and full of oxygen.

However, should the water level drop during winter, perhaps caused by the breaking of a beaver dam or some roadside construction, the icy air can now reach the once protected mud and cause body cells to freeze. Dead turtles are the result, and this has happened in more than a few cases.

A few years ago, a colony of Blanding’s turtles was all but wiped out due to a low water level. They had hibernated in a marshy area that was adjoining a Great Lake, and when the water level of the lake dropped over winter, the shallow bays became exposed and froze solid. Dead turtles, everywhere.

However, if the water remains but the oxygen level becomes depleted, turtles can then switch their internal survival system on and continue to function without oxygen. This is hard on the turtle’s body systems and potentially lethal acids can build up. To counter these acids, calcium is removed from their bones (just like me, and maybe you, taking an antacid pill to counter heartburn).

The downside to this survival technique (I’m back to talking about turtles now, not your heartburn) is that by springtime the turtle is one big muscle cramp and must renew itself by basking in the warm springtime sun.

All this appreciation for turtle behaviour was just a flash by in my mind as I dipped my paddle for a course correction. And then it hit me… the longer I drifted downstream, the harder and longer it would take to paddle vigorously to return upstream! Darn, I can feel the heartburn starting already.

Dave’s Notebook: Looks like the leaves will be hitting their peak colour around here on Thanksgiving weekend!

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© 2021 David J. Hawke

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