The Behemoth and the Butterfly; December 2008; Scientific American Earth 3.0; by Jim Cornfield; 4 Page(s)

Every winter Mexico hosts a pair of extraordinary migrations. One, a round-trip of 3,000 miles, brings the gaudy monarch butterfly from the northern U.S. and southern Canada to its winter refuge in the south-central state of Michoacán. There shafts of morning sunlight pierce the forest as millions of silent visitors, each weighing less than a tenth of an ounce, cling to branches everywhere.

Seven hundred miles to the northwest, the 36-ton gray whale completes the southward leg of a journey from Alaska¿s Bering and Chukchi seas to lagoons along the central shores of the Baja California peninsula. This pilgrimage, outbound and return, skirts 12,000 miles of coastline¿a feat generally accepted as the longest known mammal migration.