Turtles in the Winter

In thinking about my turtle story that inspired this new blog, I realized that, while it's a story I enjoy sharing, I know little about the biology behind it.  Yes, I'm aware that turtles hibernate under the ice and sometimes in the mud all winter long, but just how does a turtle survive such long, cold months?  How exactly do reptiles hibernate?

Luckily, the book I'm currently reading, Winter World by Bernd Heinrich had some answers.  In short, turtles are some of the most resilient creatures in the world, which makes sense if you think about how long they've been around.  Relative to most other animals, turtles evolved quite a long time ago.  It's possible that turtles lived right through the "global winter" of 64 million years ago that took the lives of many dinosaurs, so a measly six-months under the frozen ice is comparatively nothing.

One cool features turtles have to keep themselves alive is blood that acts as an anti-freeze.  Some turtles' bodies will completely freeze, but their internal organs are protected because the blood pumping through their bodies won't become frozen.

A painted turtle, frozen for the winter.

However, a greater problem exists in a turtles' need for oxygen.  While most animals that spend the winters under the ice have gills, turtles breathe with lungs and need a constant supply of oxygen.  Cold water retains oxygen better than warm water, so that helps.  Aquatic plants can photosynthesize and produce oxygen in the water too, but as soon as snow covers the top of a frozen lake, the plants can no longer get the sunlight they need and the rotting vegetations sucks the oxygen right back up.  The question of how turtles get their oxygen continues to stump researchers, but there are some studies out there that might provide us with some helpful clues.

One study led by Gordon R. Ultsch in 2000 investigated a colony of map turtles (Graptemys geographica) in the Lamoille River and Lake Champlain in Vermont.  They found that in winter, once the water drops to temperatures of 2-degrees-Celsius, the turtles simply pile themselves on top of each other deep at the bottom of the lake, and there they remain from November to March.  The researchers removed the turtles once a month to measure their blood acidity, lactate, oxygen, and carbon-dioxide levels.  As it turns out, the turtles remain aerobic (breathing oxygen) throughout the entire winter, simply by significantly lowering their metabolism.  This is possible because of their lack of physical movement and low body temperatures.  Furthermore, all the map turtles rested with their legs and heads fully extended, which seems to act as a way to maximize skin exposure to take up oxygen in the water.

In contrast to the map turtles, painted turtles (Chrysemys picta) hibernate in shallow water.  The advantage here is that shallow water heats up sooner in the spring, thus triggering the end of the hibernation period in the turtles.  A shorter hibernation period means a less intense impact on the metabolism.  However, shallow hibernation increases exposure to predators such as raccoons.  Painted turtles deal with this by burying themselves in the mud, but this cuts off all exposure to oxygen in the water.  It's all a trade-off.  Deep water means a longer hibernation but more available oxygen while shallow water means a shorter hibernation but with less oxygen available.

Like I mentioned, at the end of the day, the lesson is that turtles are resilient.  Hibernation takes a huge toll on their bodies, but it has worked for them for millions of years.  It's easy to forget all that's happening under the layer of ice on the lakes in winter.  If you're a turtle, it's a great place to be, but it certainly comes at a cost.

The Turtle

One of my favorite Ojibwe stories to share with students is about a turtle, a long time ago. In short, the turtle used to be best of friends with the birds, which was all well and good until the birds flew south every autumn and the turtle was left all alone for the long, cold winter.

One autumn, as the birds are gearing up for their southwardly flight, the turtle decides that he wants to come with this year. The birds don't undertand how that could be possible, since he can't fly, but he comes up with a plan. He proposes that crow and blackbird, the two strongest flyers, hold a stick with their legs. With his strong jaw, turtle will bite down on the stick, and thus the birds will carry him south for the winter.

It sounds a little silly, but the birds agree to give it a try. And for awhile, it works. The turtle sees so many amazing new things as they fly south. His curiosity is overwhelming, but he can't ask any questions because he would fall. Eventually, inevitably, his curiosity does get the better of him, and he opens up his mouth to ask crow and blackbird a question. Of course, the turtle falls down, down, down. When he hits the ground, he is so embarrassed that he crawls to the nearest river-bank, buries himself under the mud, and there he spends every winter forevermore.

In my last few times telling this story, I've come to realize that I am the turtle. The turtle was craving an adventure, the turtle was really curious to learn more about the natural world around him, the turtle was invested in his community (and the turtle really liked birds). The turtle in this story represents who I am as a naturalist.

Weaver Dunes, circa May 2011. This is me with a Blanding's turtle, quite different from the river turtle described above.

Thus, this blog. "Miskwaadesi" is the Ojibwe word for river turtle. I have recently been wishing I was recording my adventures, my observations, the things I've learned, and my stories as a naturalist. This is the place where I intend to do that. It's for me, of course, but for anyone else who's interested as well. Once more, I'm giving this blogging thing the ol' college try. We'll see what happens.