One of the world's most astounding wildlife events occurs each year in Mexico's Central Highlands, featuring the most delicate of creatures. As we enter a grove of fir trees on a remote mountaintop, the trunks and branches appear to be blanketed with rusty autumn leaves. A closer look reveals they’re quivering. Then, as the sun emerges from behind a cloud to warm them, hundreds of thousands of monarch butterflies take to the sky. Experience this moving phenomenon with expert interpretation from Mexico’s premier naturalist guides.