Monarch butterflies are not able to survive the cold winters in the United States or Canada, so like most birds they fly south for the winter. The migration usually begins sometime in October or as soon as the weather starts turning cold in North America. Monarch butterflies living east of the Rocky Mountains fly to Mexico and monarch’s living west of the Rockies fly to Southern California. Experts have not yet discovered how the monarchs can navigate to the same spots every year when no single butterfly can survive the roundtrip but most believe that flight patterns are inherited or they are capable of using the earth’s magnetic fields for orientation.
While in Mexico, the butterflies winter haven is found at the El Rosario Butterfly Reserve in the state of Michoacan. Here, the butterflies have an ideal combination of trees and plant food needed to survive until spring. It is estimated that 20 million monarchs stay in this place every year which is open to visitors interested in observing this natural event from November until late march when the northward migration from Mexico begins. As previously indicated, the length of these journeys exceeds the life span of a monarch, so the first generation will only make it as far as Texas or Oklahoma before the females need to deposit eggs for the next generation if the species is to survive. All together it requires 4 generations of monarchs to complete this annual migration pattern .