YELLOWSTONE in Winter

TO a tourist, Yellowstone National Park in winter is chillingly beautiful, silent, and desolate. For its animal population, however, cold weather and snow cover complicate survival.

Grizzlies, ground squirrels, and marmots hibernate through most of the winter, but other animals must intensify their search for food. Some migrate to lower elevations or thermal basins where temperatures are warmer, snow is not as deep, and food is easier to find.

Visitors are more likely to spot elk and bison, as the animals' winter range overlaps touristed areas. There is an economy in the big animals' movements in the snowy months: The less energy expended, the more easily they can survive.

Bison wag their wooly heads in the snow to uncover frozen grass to eat, coating their serious faces with a comic layer of snow.

Elk step silently through the powder. Regal males balance enormous crowns of antlers on their heads. The antlers can weigh up to 25 pounds. In the spring they will be shed.

Thermal pools and rivers breathe steam into the still white landscape, coating trees and rocks with ice. The hot water creates localized microclimates that support lush, summerlike plant growth even in midwinter.

Winter in Yellowstone runs from mid-December to mid-March. The only open road in the 2.2-million-acre park runs from the north entrance at Gardiner, Mont., to Cooke City, Wyo, seven miles east. Otherwise, visitors travel by snow coach (a sort of bus on caterpillar treads), snowmobile, cross-country skis, or on foot.