Each winter morning while he lived at Walden Pond, Henry David Thoreau took ax and pail and went to draw drinking water from the pond. Cutting daily through a foot of snow, then a foot of ice, he would “open a window under my feet where, kneeling to drink, I look down into the quiet parlor of the fishes, pervaded by a softened light as through a window of ground glass.”
It was the ice of Walden Pond that inspired one of Thoreau’s most moving realizations. “Heaven,” he wrote, “is under our feet as well as over our heads.”
A more prosaic naturalist, however, thinking of swimming muskrat and scuttling raccoon or, for that matter, of fish and fisherman might instead offer this observation of pond ice: “One man’s ceiling is another man’s floor.”
To the creatures that live beneath it, ice seals their watery realm off from the world above, dimming light, stilling air currents and reducing oxygen. To those that can now literally walk on the water, the frozen surface beneath their feet can serve as a tool, a trail, a toy—or a trap.
For us, the ice of the frozen pond can serve, as it did for Thoreau, as a window into lives, both above and below, that are now vastly different than in the warmer seasons.
Some pond creatures spend the winter hovering, comalike, between life and death. A carp may float motionless, embedded in a block of ice. If there is sufficient oxygen dissolved in the water, though, the fish will survive the thaw; a natural antifreeze keeps its cells from freezing and bursting. On the soft mud of pond bottoms, frogs, toads, salamanders, and turtles overwinter in a sort of suspended animation, living without drawing a breath or eating a meal. The mud is always warmer than the water; a foot beneath a mantle of ice, the water temperature might be thirty-eight degrees Fahrenheit, but four inches into the mud, it could be two degrees warmer. Although these animals don’t freeze, the temperature is cold enough to slow their metabolism; they can subsist on the tiny amounts of oxygen dissolved in the water, which they absorb directly through their skin.
But all is not quiet below the ice. As Peter Marchand observes in his book Life in the Cold, “Maybe the hardest thing to accept about winter is that it is so alive.” Sometimes, when a slow freeze creates ice free of clouding air bubbles, you can see through the ice as if through a glass-bottomed boat and watch fish swim vigorously beneath your feet. If you’re very lucky, you might even glimpse a muskrat through the ice, swimming underwater with its back feet, holding its front feet under its chin and trailing a stream of pea-sized bubbles. Likely there may be mink there too, swimming beneath the ice, looking for the muskrat.
Even when the ice is thick and clouded, you can still tell much about the creatures of a pond by looking at, rather than through, its surface. Especially after a light snow, tracks and other signs of animals show up brilliantly on the ice of a pond. Water, even though frozen, is a powerful magnet for animal life.
This is one reason why Susan Morse, a forester specializing in wildlife habitat who teaches at Burlington College and the University of Vermont, leads her students to beaver ponds for her winter ecology seminars. For it is here, on the surface of the frozen pond, that you can see “the whole forest waking up and doing things and getting out and having fun.”
No one is having more fun than the otters. As well as swimming beneath the ice (where they hunt for fish and probe the bottom for hibernating amphibians), they are also sliding over the slick surface, using their bellies as toboggans. (In fact, the troughs they make in the snow look so like the imprint of a child’s toboggan that even Donald and Lillian Stokes were once fooled when they noticed one such trough that ran straight across a parking lot. When they saw the slide went directly into very dense underbrush, they realized what had made it.)
Cheerful daredevils, otters will use the rapids of a river—the last areas to freeze and the first to thaw—to slip under the ice. Morse has come upon their sign, incredulous: “Great chunks of ice, jags of ice sticking up like teeth, and there it is, a great big otter track. And sure enough, it disappears under the rapids”—perhaps the otter wanted to enjoy the racing water. Otters are so funloving that they are even known to keep playthings in their dens—stones or shells which they like to drop through the water and then chase.
Beavers have more serious business in mind this time of year. They have worked hard to make their winter livelihood possible. In a carefully built stick-and-mud lodge, a huddled family of beavers (mother, father, and kits of the last two years) may enjoy temperatures up to forty degrees warmer than the air outside. Together they have cut up to four cords of stem wood for their winter’s rations, sunk with its own weight and stored in their giant underwater refrigerator.
But in spite of the beavers’ best efforts, food may run out before winter’s end; if so, you may see where they have slipped between the melted edges of pond ice to harvest trees and then drag them back under the ice. Though these “tree trails” obscure the beavers’ tracks, there is little doubt what made them.
All this activity above, around, and beneath the ice makes the pond a grocery store for predators. One winter, Morse found the evidence of a really big cat-and-mouse game: a bobcat’s prints by the shore; a beaver’s tree dragged into the ice; then the wide pawprints, claws out, of a thirty-pound cat struggling to pull a thirty-pound rodent across the ice.
To some creatures, the ice is the door to a refuge; others use ice as a trap. Hooved creatures normally avoid slippery surfaces. As Morse says, “Their feet are all wrong on the ice—it’s like walking in high heels.” Wolves and coyotes know this; and this is why they will sometimes drive their prey out onto the ice, as a pair of coyotes did on a pond near Morse’s Jericho, Vermont, farm one winter. She read the struggle in the skift of snow atop the ice. From the prints, she could tell the deer carcass later also fed ravens, blue jays, and foxes.