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Newts from the Field: Secrets of the Frozen Swamp

By Shelby Perry

Every season is my favorite season, but right now I could not be more excited about the coming of winter.  As the snow dampens noise, the hushed forest takes on the feeling of a library: filled with quiet knowledge and adventures just waiting to be discovered. 

Oh winter, I forgive you for freezing my eyelashes shut on morning walks, for your short days and plentiful hours of darkness, for the months of unrelenting cold, because during winter there are surprises everywhere. 

Photo by Mike Pryzbala.

Take for example, the frozen swamp.  Like books in a library, the elements of a frozen swamp appear innocuous and perhaps even boring upon first glance – but tuck in to any piece for more than a moment and you’ll find drama, danger, and maybe even a little magic. 

The Surface of the Swamp

Flat expanses of snow-covered ice are not uncommon in beaver wetlands, like those found on the Sawtelle Addition and the Binney Hill Wilderness Preserve in New Ipswich, NH.  A mid-winter visit might look like little more than trees and a field, but be careful! 

Beaver wetlands are notoriously dangerous for their unpredictable ice layers and deep channels of water beneath.  Because beavers actively roam beneath the ice all winter long, their movements, combined with changes in water flow, affect the way ice forms on the surface of the pond.  Though dangerous for larger mammals like moose, deer, and people, smaller animals can safely cross the ice, leaving their stories behind in their tracks.  A hungry coyote checks out the beaver dam, a tiny mouse forages for food, and an owl imprints her wings upon the snow when she grabs that mouse for a midnight snack. 

Tracks show that a fox safely crossed over the ice just after a light snow.
Photo by Shelby Perry.

Reading these tracks can tell you a lot about a swamp – who lives there, and who is passing through.  Who is still out and foraging, and who is tucked away for a winter nap.  Experienced trackers can even read details like how long ago the track was left, where the animal stopped to listen, or when they hurried up to escape danger. 

Beneath the Ice

Sometimes, if you are very lucky, there is a window in the ice through which you can peer into the world beneath.  This is where the real magic lies. 

Beneath the ice there are more than just beavers.  Minnows flit here and there, specifically adapted to moving quickly in cold water.  In the shallows of frozen ponds, air-breathing turtles pass much of the winter buried in the mud, away from freezing air and hungry predators.  Though they are safe from being eaten, their internal systems rest in a precarious and delicate balance to stay alive until they can surface and breathe again in the spring. 

Turtles hardly move for the entire winter, so their metabolism slows to a crawl and their need for oxygen decreases.  Early in the winter, when sun sometimes shines through the ice, aquatic plants can still photosynthesize.  The oxygen they exhale is trapped beneath the ice, and readily dissolves into the water.  Turtles and amphibians under the water absorb that oxygen because the difference between the higher oxygen levels in the water and the lower levels in their muscles creates a natural pull, drawing it in through their skin.

Turtles can survive the winter living under the ice without access to oxygen for several months.
Photo by Shelby Perry.

When the snow gets too thick and blocks the sunlight, the plants die back and the turtles need a new strategy to survive.  Some species, like painted turtles, can borrow minerals from their skeleton that are basic (have a high pH) to neutralize the lactic acid that builds up in cells when there isn’t enough oxygen.  This lactic acid build-up is the same thing that causes cramps in tired muscles after a long run or difficult hike.  Were it not for this clever trick, the pH of the turtles’ bodies would become fatally acidic.

According to the book Winter World by Bernd Heinrich, the amount of time a turtle can go without oxygen varies by where the turtle is from.  A painted turtle from the American south cannot go nearly as long as the painted turtles local to the Northeast.  This suggests that turtles have adapted winter survival strategies specific to their latitude.  Amazingly, our native turtles can live for up to 30 years, even though they spend around a third of their lives almost completely deprived of oxygen!

The miracles of winter survival are many. Animals hibernate, live under ice, hunt through the snow, store up fat and food, and camouflage themselves. And when we choose to slow down, brave the cold, and take a close look, winter will reward us with its ingenuity and magic.

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