One of the greater mysteries of nature is the annual migration of Monarch butterflies from the northeast United States and Canada to the Transvolcanic mountain range in Michoacan, Mexico. An estimated 200-500 million Monarchs arrive in the high elevation in late October where they winter in a semi-hibernation state until the warm winds of March awakens them to begin migration north, feeding on milkweed and breeding as they go.
Scientists believe no single butterfly makes the entire two-way trip, rather it is thought three to five generations are necessary to complete the cycle.
Scientists also do not fully understand how or why the Monarchs make the 2,500 mile multi-generational migration, nor do they know why the dense growth of fir trees 8,500 feet up in these particular mountains attract them.
On arrival the Monarchs settle in the thick boughs of fir trees and cling motionless in huge numbers unless disturbed or prompted by changes in temperature to move up or down the mountain.
Naturalists only discovered in the 1970s that Monarchs migrated at all when they stumbled across their remote Mexican mountain destination. Now a butterfly sanctuary has been established near the village of Rosario for the protection and study of the species.
In the folklore of the Aztecs, the native people of Northern Mexico, Monarchs were thought to be the souls, reborn, of fallen warriors wearing the orange and black colors of battle.
Like most wildlife the primary threat to existence is loss of habitat. So too are Monarch butterflies threatened. Illegal logging in the region has resulted since the 1970s with nearly 50-percent of their wintering grounds destroyed.
An unusually harsh winter in 2002 with heavy rains and a killing cold caused an estimated 75-80 percent that winters population of 200-500 million butterflies to perish. But scientists believe the species survived that decimation and has recovered. Numbers of migrating Monarchs in recent years have returned to normal.