On Winter Perseverance of our Cold-blooded Friends

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Today marks the 180th day in a row I have had snow in my front yard. Most had melted as of mid-April and all that remains is what piled up under the edge of my barn roof, and that too shall pass in the coming weeks. Yet it was that point around mid-April that I began to question, once again, why I, as a herpetologist, would choose to live in a place where you can’t actually see frogs, salamanders, turtles, or snakes for almost half of every year. And in the entire state of Vermont, we only have about 40 species reptile and amphibian to begin with, which, compared to a state such as Georgia and its 170 species, sometimes prompts the same question from myself and my colleagues smart enough to live in the south. While I could drone on about the endearing qualities of the Northern Vermont landscape that make it all worthwhile, the answer that resonates most with fellow “herp nerds” is that our harsh winters are actually the very reason for many of the aspects of northern herpetology I find most fascinating.,

Most mole salamanders emerge to breed early in the spring, even if there is still snow on the ground.
Spring amphibian migrations can be very large in the north. One long-term monitoring site, for example, has been known to have over 1000 Blue-spotted Salamanders cross in a single night, along with hundreds of Four-toed Salamanders. Such large numbers of salamanders all moving at once is only possible thanks to our long winters.

Some of my most memorable moments in the field involve trudging through mixed precipitation in late March with nothing but a rain jacket, flashlight, and hundreds of salamanders to keep me company. These “big nights” take place in the south too, but the pent up reproductive energy caused by a long winter results in frogs and salamanders migrating across roads on the first warm, rainy nights of spring in numbers almost unheard of in the southeast. And if it weren’t for our long winters, Timber Rattlesnakes would not den en masse in just a handful of locations in the southern Champlain Valley, Wood Turtles would not congregate along valley streambanks every spring and fall, and Gartersnakes would not pour out of select rock crevices by the dozens (or even hundreds) in April to form breeding balls. Winter conditions here push the limits of survival for any cold-blooded animal, and because the places these animals use to seek refuge might be different from where they forage in the summer, the changing of the seasons results in remarkable micro migrations across the landscape.  Picking the right spot to survive the winter is only half the battle though, these animals also need to endure.

Gartersnakes emerge from their underground shelters very early in the spring, even when there is still snow on the ground.
Some time in March or April, Gartersnakes emerge from their winter refugia to mate, sometimes in very large numbers, forming "breeding balls" that I have been fortunate enough to witness only a couple times.

Burrowing a few inches or so below the leaf litter, Wood Frogs are able to avoid the harshest temperatures winter has to offer, but the ground around them still freezes, and the frogs need to somehow survive that. By concentrating sugars into their tissues and vital organs, they are able to “supercool”, allowing their body temperature to drop below freezing without actually freezing. Of course that only works to a point, and eventually the frogs freeze almost entirely solid except for their hearts and livers where sugar concentrations are the greatest. Then, when they thaw, they do so from the inside-out such that as each organ thaws circulation is immediately restored, avoiding cellular deterioration. This trick allows them to overwinter close to the surface and “wake up” before other species, which is important because the vernal pools Wood Frogs breed in dry up in the summer, so they need to migrate to the pools as early in the spring as possible if their young are to survive.

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A Common Snapping Turtle bursts from the ground after a reservoir was drawn down in the early spring. This turtle had burrowed into the muck for the winter, deliberately cutting itself off from oxygen, perhaps for months.

Painted Turtles overwinter in lakes and ponds that ice over, but standing water is prone to oxygen depletion in the winter, a condition known as anoxia. At near freezing temperatures, a Painted Turtle does not need to breathe air because it can absorb all the oxygen it needs through the roof of its mouth and lining of its cloaca (also known as “butt breathing”), but only if there is oxygen to be had. When water becomes anoxic they instead metabolize glycogen from their muscle tissue, resulting in lactic acid building up in their blood. The acidity would kill most animals, but Painted Turtles leach calcium from their shells as a buffer, staving off death for a considerable length of time. In laboratory experiments Painted Turtles have survived over 130 days with no oxygen at all. For humans the record is 40 minutes before the resulting brain damage is fatal, usually much less.

Mudpuppies (foot-long, fully aquatic salamanders found in the Champlain Basin and Connecticut River) avoid freezing temperatures by never leaving water and are actually most active in the winter. Nobody really knows why.

Each species has their own tricks, and every herpetologist needs a little time to write grants, submit reports, and catch up on data analysis. Personally, I am glad to share the Northern Vermont landscape with species much better adapted to surviving the cold. With the month of May now upon us, vernal pools have sprung to life, snakes have started to venture away from their hibernacula, and the stream banks, once again, are lined with Wood Turtles. Summer is coming, and I am more than ready for it.

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For the next month, select stream banks will be lined with Wood Turtles, which would be nearly impossible to find were it not for the risk of morning frost forcing the turtles to stay near the streams they overwintered in.