These clouds don't signal rain. They are vast smoke plumes. Yellowstone is burning. Throughout the summer, the dry lodgepole pines have become like a tinderbox and lightning has struck the match. In 1988, a third of Yellowstone burned in a single summer. Animals that depend on these forests will starve this winter. But Yellowstone itself has a longer perspective. Ashes fertilize the soil and fire opens it up to sunlight. As the forests regenerate, new life finds opportunity. In August, fledgling hummingbirds gorge in fields of fireweed that have risen from the forest's ashes. For them, the summer is already nearly over.

They must chase the sun south before winter returns.