A Northwoods Almanac for 1/16-29/ 2026

 A Northwoods Almanac for 1/16-29/ 2026  

 

Adult Painted Turtles Extreme Responses to Winter

            Cold-blooded animals (better referred to as “ectotherms”) like reptiles and amphibians have to go to great extremes to survive northern winters. Even mild freezing temperatures will cause the water inside their bodies to expand and freeze, the sharp ice crystals potentially shredding cell membranes and rupturing the cells, leading to a quick death.

            Thus, every species of ectotherm has had to evolve a strategy to make it to spring, and sometimes even within a given species, the strategy may differ. Take, for instance, painted turtles. Adult painted turtles can’t survive below-freezing temperatures, and adapt by typically ensconcing themselves onto lake or river sediments prior to ice-up and waiting out the winter.

            The minor problem with this strategy is that turtles breathe via their lungs, and lungs, if you haven’t noticed for yourself, don’t work underwater. To survive, painted turtles drop their internal body temperatures to the same as the water, usually a few degrees above 32°F, and their

metabolic rate drops by about 95%. This reduces their oxygen demand so much that they usually can get all the oxygen they need by respiring through their skin, especially the skin inside and around their mouth as well as their cloaca (less scientifically called “butt breathing”).

Turtles under ice

            But oxygen levels in shallow lakes often crash as the winter progresses (a process called “anoxia”), which can kill fish, reptiles, and amphibians. At this point, painted turtles are unable to get any oxygen via “butt breathing” and compensate by dropping their metabolism to just 1% that of summer levels. Now with no oxygen available whatsoever, they start burning glycogen from muscle tissue to produce enough ATP (Adenosine Triphosphate, the fundamental energy currency for all cellular activities) to power their cells. 

            Now, however, a new problem arises. Lactic acid is produced as a byproduct and steadily rises during periods of anoxia, eventually leading to a condition called anoxic acidosis, which leads to an eventual death. Of all the turtle species in North America, painted turtles have the greatest tolerance to anoxia and the resulting acid buildup. They balance out the lactic acid by precipitating calcium and potassium from their skeleton and shell into their blood stream, which buffers the acidity and staves off the symptoms of acidosis. 

            Remarkably, they can survive without food or oxygen for 100 days. One study found that painted turtles can reduce their heart rate to 8 beats per hour, or 1 beat every 7 ½ minutes.

            Even so, some adult painted turtles die after prolonged periods in anoxic conditions. The best solution for defeating anoxia is to have an early ice-off so atmospheric oxygen can mix with the water. So, while early ice-off is great for anglers, or for those of us starved to see open water, it can be crucial for adult painted turtle survival.

            

Hatchling Painted Turtles Do Something Different, But Equally Extreme

            Painted turtle hatchlings offer a different story. Painted turtle eggs typically hatch in the early fall and the tiny hatchlings head immediately for open water. But some hatchlings remain in their shallow underground nest all winter, and are regularly exposed to freezing temperatures that kill adults. 

            To survive, the hatchlings have evolved two methods of coping with the freezing temperatures. They can “supercool,” a process by which liquids in the turtle’s body drop

to well below their normal freezing points without actually freezing. It’s basically like using an antifreeze, but in this case using high concentrations of glucose and other cryoprotectants

(compounds that protect tissue from freezing conditions). High glucose concentrations can allow the hatchlings to remain unfrozen down to an average of 14°F. 

            There are variables, however. The moisture in the soils and the type of soils surrounding the nests impact the temperature to which the turtles can supercool. In wet sandy soils,

turtles can only supercool to about  28°F before freezing, but in clay soils they can chill to 9°F, the difference being with how ice crystals form in the different substrates. 

            The second strategy they use is extra-cellular freezing whereby water is drawn out of the cells and into the spaces between the cells where it can freeze and expand without rupturing the cells. All but the liver and other vital organs freeze solid and can remain so for several days without causing harm to the hatchlings. 

            Bottom line: For most of the winter, the hatchlings utilize supercooling because they can’t tolerate long periods of being frozen.

            Come spring, the hatchlings will emerge and head for the nearest water.

            Amazing!

 

Garter Snakes Can Freeze, Too!

            Well, turtles don’t have the market cornered on freeze tolerance. Common garter snakes typically swarm together in an underground site called a hibernacula where they can freeze, too (they are known to also spend the winter underwater). They, too, are capable of supercooling to about 23°F, though this apparently isn’t an adaptation to winter freezing, but rather to freezing in the spring when they have emerged from their hibernacula and there’s an overnight frost. They can only freeze for a short period, around 10 hours, but that’s enough to get them by, and explains why garter snakes range so much farther north than other snake species – as far north as the southernmost tip of the Northwest Territories in Canada. 

Common garter snake range map

 

Some Species of Northern Frogs Also Freeze!

            Four out of our nine native species of frogs in the Northwoods – spring peepers, wood frogs, Eastern gray tree frogs, and boreal chorus frogs – also freeze over the winter. They freeze via a very similar mechanism to that of hatchling turtles, drawing water out of their cells so that freezing occurs outside of cells rather than within. 

            These frogs appear from the outside to be entirely frozen, their skin and eyes rock hard and most of their bodies solid – about 60% frozen. Their liver and heart, however, remain in a super-cooled state, though the heart ceases to beat and no breath is drawn. Basically, they’re in a state of suspended animation, appearing totally dead to the world.

Frozen wood frog

            Then in mid-April, they begin to thaw, and something yet more remarkable happens. In the fall, they freeze from the outside to the inside, but if the frog’s tissues and organs thawed in that same order, the frog would die. The skin, limbs, and eyes would thaw out without being connected to a beating heart, and tissue on the frog’s exterior would become necrotic – dying due to no blood flow.

            Instead, the frogs thaw from the core outward, starting with the heart beginning to beat. As each subsequent layer of tissue thaws, blood flows to the tissue until the skin and eyes soften, a process that only takes a couple hours. And then they can begin calling. and the

frogs can resume normal body function immediately afterward.

            Winners of the award for the most frozen of all organisms, wood frogs in Alaska were found to survive freezing to temperatures as low as zero and remained frozen for upwards of 200 consecutive days. Those Alaskan frogs concentrated ten times the amount of glucose in their musculature compared to Wood Frogs studied farther south.

            It should be noted that these four species of frogs overwinter in upland forests under leaf litter, logs and tree roots while air temperatures regularly fall way below that  in which the frogs can survive. But the frogs survive because of the snow cover that insulates them those microhabitats, providing yet another reason why having good snow depth beyond skiing and snowmobiling is important in the North country.

            BTW, where do our other five species of frogs overwinter (mink frogs, leopard frogs, green frogs, bullfrogs, and American toads)? Except for toads, underwater. Toads dig down into loose soil to below the frost line and spend the winter underground.

             

Sightings – Leucistic Black-capped Chickadee and Northern Shrike

            Zach Wilson sent me a photo of a leucistic black-capped chickadee that is coming to a feeder on the Turtle Flambeau Flowage. If you’re not familiar with leucism, it’s a partial loss of pigmentation in animals, causing patchy coloration.  

Leucistic black-capped chickadee, photo by Amanda Griggs

            We continue to have a northern shrike perching atop a large silver maple and overlooking our bird feeders. Our songbird numbers have been low so far this winter, and I suspect the shrike’s predilection for eating songbirds is partially responsible for that.

 

Great Lakes Ice Cover

            Great Lakes ice coverage stands at 14.43% as of January 05, 2026. What the future holds for ice formation depends entirely on the weather. Prolonged periods of below freezing temperatures and calm winds enhance ice formation. High winds, warmer temps, and wavy surfaces inhibit ice formation.

 

Celestial Events

            Our days are growing longer now by more than two minutes per day.

            The new moon occurs on 1/18.

            The year’s coldest days on average occur between 1/20 and 1/29, though the first week of February has a history of also being pretty brutal.

            On 1/23, look after dusk for Saturn about 4° below the waxing crescent moon. 

            Best planet watching for the rest of January? Jupiter rises in the east at dusk at -2.7 magnitude, so it’s the brightest star in the night sky these days. And Saturn (1.1 magnitude) is high in the south at dusk, then setting in the west.

 

Thought for the Week

            “ In winter the stars seem to have rekindled their fires, the moon achieves a fuller triumph, and the heavens wear a look of a more exalted simplicity.” –  John Burroughs, "The Snow-Walkers," 1866

 

Please share your outdoor sightings and thoughts: e-mail me at johnbates2828@gmail.com, call 715-476-2828, snail-mail at 4245N State Highway 47, Mercer, WI, or see my blog at www.manitowishriver.blogspot.com