The Monarch butterfly migration east of the Rocky Mountains is one of the world's magnificent natural events. Adult Monarchs that emerge from their chrysalis in early Fall will fly from the United States and Canada to overwintering grounds in Mexico, some traveling as far as three thousand miles. These are the only butterflies in the world to make such a long, two-way migration each year.

In fall, Monarch butterflies from east of the Rocky Mountains return to high-altitude oyamel fir forests in central Mexico, where millions of individuals overwinter in extraordinary aggregations. These Monarchs begin migrating north in March and early April to the Gulf Coast of the southeastern United States, where the females lay their eggs on milkweeds. One to two generations of Monarchs are produced in the Gulf Coast States in the spring. These offspring of the wintering generation continue northward without their "mothers" to recolonize the northern breeding range. Because southern milkweeds die in June, the migration must continue north to utilize the milkweed resources of central and northeastern North America. This allows Monarchs to produce up to three additional summer generations. The cycle then starts over in fall when this new generation of Monarchs heading south.

Despite this unique life history, neither the United States nor Canada has protected any habitat along the major migration corridors for Monarchs. Mexico has protected only tiny fragments of the habitat to which the Monarchs migrate. Because so little protection is afforded these butterflies, the annual migration of the Monarch in North America has been recognized as an endangered biological phenomenon. For more information on Monarchs in Mexico, go to http://www.monarchwatch.org.