Walking Hibernation  By Joanne Merriam  The tundra buggy, a
Hummer-like vehicle on thousand-pound tires that kept its
passengers five or six feet above the heads of the polar bears,
bounced over a rock submerged in the snaking, slushy river
previous trips had created. Jennifer felt it in her spine.  "You
okay?" she asked Don, and he nodded absently, his attention
wholly focused on the bears lying in the snow several yards
away. One of his hands was bunched up in a fist, which he held
in a sustained punch against the back of the seat in front of
them, balancing on his bony knees on her lap. The buggy rocked
to a stop with a final squelch, and Jennifer turned on her
camera.  A willow ptarmigan flew overhead. She focused
carefully: click, ptarmigan. Click, bear against snow. Click,
bear raising muzzle. Click, Don watching bear. Click, sullen
sky, and Hudson Bay in the distance.  The bears opened their
mouths, breathing soft clouds. Their fur, faintly yellow against
the blue-white of the snow, looked soft, too, t