By Kristina Nininger, Naturalist at Kroening Nature Center
Who roams under the snow? If you look closely on a winter hike in the park, you may be able to spot a tiny hole, a tunnel entrance just below the surface of the snow. Follow that tunnel and you’ve just crossed over into the subnivean zone (sub for below, niv for snow)! There, a fragile space forms between the soil below and the snow cover above, and hosts a parade of tiny mammals moving and living their winter lives unseen. The air there is tolerable for mice, voles and shrews, remaining a relatively temperate 32°F no matter the frigid, sub-zero temperatures above. The snow actually acts as insulation, so the more snow, the better for the subnivean zone and its inhabitants.
Some mammals can keep moving to beat the cold, but what can a tiny, moist-skinned, cold-blooded amphibian like a frog, toad or salamander do when the weary winter weather comes? And what about our native snakes and turtles? These creatures have a few incredible strategies to survive the coldest of the cold.
Counterintuitively, many frog species, like the wood frog, actually survive the cold by freezing! Their bodies shut down and use glucose, or sugars, as antifreeze to keep ice crystals out of their organs. They’ll remain partially frozen in the leaf litter for the entire winter, and then thaw out to return to life in the spring. Some species, like northern leopard frogs, spend the season underneath the ice in lakes or rivers. They take oxygen from the water and will usually sit at the bottom in a group, but you may see them swimming around if the ice is clear. And other species, like the American toad, instead go underground, backing in below the frost line by digging with their hind feet.
A salamander’s body may be shaped like a lizard, but these animals are more like frogs than scaly reptiles. Appropriately enough, “mole” salamanders, such as the mysterious spotted salamander, spend most of their time underground in all seasons, and little is known about their wintertime habits. They can’t survive freezing, but they know how to keep themselves out of the cold until things warm up. However, they will be out again in early spring to breed, even if it means braving some snow on the ground!
Many turtle species will overwinter underwater, buried in the mud at the bottom of lakes and rivers where the water doesn’t freeze. Hatchling painted turtles, on the other hand, will stay on land and instantaneously “supercool,” or freeze almost completely solid, on contact with ice!
Most snakes prefer to lay low below the frost line in crevices, rotting stumps, or even cracks in building foundations. They’ll spend the winter there, occasionally coming out on warmer winter days to get some sun.
When you prepare your yard in the spring, you can help local amphibians when you:
• Watch what you’re adding to the waterways. Amphibians can be easily affected by pollutants
including lawn pesticides.
• Plant native plants. Native species support more native insects.
• Provide cover or places to hide and add water. Birds will appreciate these features too!
Be sure to join us at the Kroening Nature Center this winter for select programs and more! Visit minneapolisparks.org/nature for details and to register.