As we crest the ridge and enter the grove of evergreens, the air is still. Could this be the butterfly sanctuary, atop a fir-forested mountain in the highlands of Central Mexico? Looking closely, the trunks and branches appear to be blanketed with rusty autumn leaves. But they’re quivering. And then, as the sun emerges from behind a cloud to warm them, tens of thousands of monarchs come to life, taking to the sky in a flutter of orange, so many that we hear the humming of their gossamer wings, backlit by the sun against the blue backdrop. Sometimes, they even float down to alight on our hats and shoulders. Join our small group to experience this moving phenomenon, enhanced by Mexico’s premier naturalist guides.