This is an updated version of a story first published on April 20, 2025. The original video can be viewed here. Earlier this year we reported on one of the most remarkable and mysterious migrations in the natural world occurs every spring from Mexico to the United States. Tens of millions of monarch butterflies are on an epic aerial journey home. They've spent the winter hanging out in trees in a forest on a remote mountain in Mexico, resting up after flying all the way from Canada and the northern U.S. where they were born. It's believed monarchs have been making this journey for thousands of years, but there's a lot fewer of them than there used to be. The population in Mexico has declined 70% in the last 30 years. We arrived there in February, just in time to watch the monarchs emerge from their slumber, and begin to take flight. The monarchs come to these mountains in Michoacan in central Mexico starting in late October. Anderson Cooper: Do you still get excited going up to see them?Jorge Rickards: Every time. There's no substitute.One of our guides Jorge Rickards is the director of the nonprofit World Wildlife Fund in Mexico. Jorge Rickards: We are going to leave the horses walk a little bit, very, very carefully and very quietly so we won't disturb the butterflies.