Every fall, a magical event takes place—the annual monarch migration to Mexico. Perhaps traveling over your own head right now—or clustered by the hundreds in a nearby tree—monarchs are on the move. By instinct alone, they migrate to the mountains in Mexico where they’ve never been before.
These incredible creatures travel between 80 to 100 kilometers a day: it takes them about two months to complete their journey. The farthest ranging monarch butterfly recorded traveled 427 kilometers in one day!
The monarch is the only butterfly known to make a two – way migration as birds do. These butterflies cannot survive the cold winters of the northern climates; the environmental hints give the monarchs their cue to start their journey to a warmer place. They use a combination of the air currents and thermals to travel the long distances.
The Monarch butterflies in the eastern part of the United States travel to the Sierra Madre Mountains of Mexico and the ones that live in the western part of the continent travel to The Golden State of California. The following spring, these butter¬ies leave their overwintering sites and fly northward to lay their eggs on milkweeds and a few other plants in the dogbane family. In Florida, some non-migratory individuals remain and breed year-round.
Scholars are still investigating what guiding aids monarchs use to find their overwintering location. It appears to be a combination of directional aids such as the magnetic pull of the earth and the position of the sun among others, but not one in particular.
Monarchs group together to stay warm. Tens of thousands of monarchs can group on a single tree. Although monarchs alone weigh less than a gram, tens of thousands of them weigh a lot. The trees are generally able to support the clustering butterflies, but sometimes branches break!
The Eastern North American Population Goes Wintering in Mexico
The eastern population of North America’s monarchs hibernates in the to mountain areas in the States of Mexico from October to late March.
Monarchs stay for the winter in the Oyamel fir forests at an elevation of 2,400 to 3,600 meters (nearly 2 miles above sea level). The mountain hillsides of Oyamel forest provide an ideal microclimate for the butterflies. Here temperatures range from 0 to 15 degrees Celsius. If the temperature were lower, the monarchs would be forced to use their fat reserves. The humidity in the Oyamel forest assures the monarchs won’t dry out allowing them to conserve their energy.
Western North American Population Goes to Sunny California
Monarchs living west of the Rocky Mountain range in North America overwinter in California along the Pacific coast near Santa Cruz and San Diego. Here microclimatic conditions are very similar to that in central Mexico. Monarchs roost in eucalyptus, Monterey pines, and Monterey cypresses in California.
