The wondrous flight of millions of monarch butterflies from their roosts in the Sierra Madre mountains of Mexico has long captured the imagination of scientists, nature lovers, and tourists. Each spring, the butterflies begin their remarkable journey north. They travel thousands of miles on a trek that provides them with optimal breeding conditions and ultimately ensures the survival of the species. This video segment from Nature captures the butterflies' spring awakening.

This video is available in both English and Spanish audio, along with corresponding closed captions.