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By Root 1291 0

has extensively studied snow cover at the Center for Northern Studies in Vermont and elsewhere, has wondered how organisms that are buried under snow get their cue to start growing or breeding. How do they know, as they appear to, that the snowpack is about to melt off? Do they sense the sunlight? To investigate this problem, Marchand and his students studied the light-transmitting properties of the snowpack, finding that as the snow became increasingly more compact, it extinguished more and more light. But only up to a point. To their surprise, they found that when they mimicked the melting and refreezing that occurs in the spring when snow density increased, the snowpack became almost icelike in consistency. Then, despite or because of its greater density, it transmitted more light. Marchand speculates that this snow-penetrating light is sensed by the voles and stimulates them to start reproducing, thereby giving them their legendary reproductive potential. Alternatively, the plants detect the light first, and by growing, produce chemicals that then give the animals that eat them an indirect cue that then stimulates their reproductive activity.

For some animals in the winter woods, the subnivian zone is never totally separate from the subterranean zone. If it were fully separate, then few small mammals would survive the winter, because in some years subzero temperatures occur a month or two before there is an appreciable layer of snow. During these times, the shrews and voles inhabit the space under the leaf mold, or they live in rotting stumps that are riddled with cavities. At times they also burrow into the soil, living beneath the frost line. Still other animals, such as the molelike short-tailed shrew and the star-nosed mole and its cousin, the hairy-tailed mole, stay there permanently. The presence of the subnivian zone merely raises the frost level and allows them to be closer to the surface of the ground, where there are likely more insect prey.

While the snowpack is a haven for many small animals, it provides a severe challenge to the larger ones that hunt them for a living. Some predators would be unable to live in the north in winter if it were not for their specialized ways of hunting the subnivian prey. These winter-active hunters include the aforementioned weasels, foxes, and coyotes, and the great gray owl.

Foxes and coyotes locate mice by sound and pounce on them by crashing with their front paws through the snow. Their bouncing collapses the rodents’ tunnels, temporarily trapping the intended victim. Great gray owls (Strix nebulosa) also have acute hearing and can detect a meadow vole’s movements under snow from thirty meters away. Drawing near one, they plunge from twenty-five feet in the air, and with their balled-up feet can punch through crust thick enough for a person to walk on. They then catch the mice that are temporarily detained by the collapsed snow by repeatedly clenching their toes, sifting through the snow with their long talons. Great grays are among the largest of all owls, being nearly three feet tall, but a large part of their bulk is composed of thick layers of insulating feathers. They are not as powerful as great horned and snowy owls that specialize on hares. In calm weather the grays hunt both at night and during the day, and temperatures as low as -43°C do not cause them to leave their northern haunts. They do leave regularly, though, when their prey is depleted due to disease or overhunting. Rodent population crashes in one area do not preclude population explosions in another, and so the owls wander widely. So I too wander, a hunter of winter marvels.

03

A LATE WINTER WALK

Today, the sixteenth of March 2000, is the day before St. Patrick’s Day. It is still winter. In Vermont where I teach at the university, we are only three-quarters through the woodpile, our stash of stored solar energy collected by trees. Not a single sprig of new green is yet in sight in all the woods; the leaves, the most efficient and most beautiful solar collectors ever devised, are not yet