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By Root 1297 0

snowfall events. For example, I routinely see almost no hares’ tracks in the woods of western Maine after early snows in late October and early November, although their tracks are common in the same year and at the same sites in December. I had first suspected that the hares might migrate, until I happened to walk one November up on the ridges of Mount Bald near my camp. A hare could get up there in minutes. Here in the spruces near the top, I suddenly found many hare tracks, making me wonder if the molted animals move up into the hills where the snow comes earlier, and then later come down after the first snow falls in at the swamps, their preferred habitat.

In March the hares’ white fluffy winter fur begins to drop out and is again replaced with the summer brown. Golden-crowned kinglets take advantage of this fortuitous timing of the hares’ coat change to gather the cast fur for insulating their nests.

The hares’ winter survival depends not only on ability to hide, but also to run when needed. Unlike many animals in winter they can and do stay lean, accumulating essentially no body fat, because food is almost always within reach and food energy need not be stored. Being lightweight and big-footed gives them an advantage for moving quickly on the snow. But sinking in even a little bit slows a runner down. Yet there is a limit to how big the feet can be before they hinder rather than enhance running speed, and snowshoe hares are probably already close to as light-and big-footed as they can get. They have, however, another behavioral trait that is apparent at a glance (the patterns of their tracks in winter woods): hares follow others’ tracks and thus pack down the snow, making well-trodden highways. Hares traveling along these paths then clip the twigs along the way, and knowing the paths well, get the jump on any predator giving chase.

The snow can be an enemy, too. Small animals in the subnivian zone, that area in or under the snow, can at times be sealed in when the upper snow surface melts in the sun and then freezes at night into a solid crust. Grouse sometimes get trapped under the crust and become prey to foxes. Shrews that emerge onto the crust and do not quickly find a hole back down to safety, may be taken by a predator or simply freeze to death.

Polar bears have nothing to fear from the crust. They dig their dens into drifts of snow where they have their cubs, suckling them in warmth and safety, and hibernate for the six months of the arctic winter. My Winter Ecology students, like polar bears and Athabaskan hunters, also make temporary shelters in mounds of snow.

Every winter I take ten to thirteen students with me to my camp in the Maine woods, where we live in my homemade log cabin (two-story) that is without electricity but with a woodstove. We get water from snow we melt, or from a well at some distance. We bake our own bread and have been known to fry our own voles. We take long unstructured walks through the woods in the first week. In the second two weeks everyone settles on an independent research project that I guide. The hard part comes when everyone gets back to campus during the spring semester and analyzes their results and writes their scientific reports.

Building snow shelters is not one of the official projects. But we occasionally make them nevertheless. We start by heaping up a great pile of snow. A few hours after the snow has been heaped up, ice crystals interlock and combine to make a solid mass that can then be excavated to produce a snug and warm cave for overnighting.

Near the top of any snowpack, the snow gets denser as the crystals bond together. Meanwhile, close to the ground, where it is warmer than at the surface, water vapor from disintegrating snow crystals migrates upward and recondenses and freezes onto the upper snow pack crystals. In time, the growth of the upper ice gains at the expense of the lower, and a latticework of ice pillars and columns and extensive air spaces at ground level create the subnivian space that is, in a sense, a continuous snow cave inhabited by