Monarch Migration--The Changing Compass
Several times in previous Dandy Design sections of this journal, we have talked about the migration of various kinds of life. We have seen that birds, turtles, whales, eels, caribou, and even some insects accomplish incredible migrations over great distances. One of the more interesting migratory patterns is that of the monarch butterfly, which moves from a 40-mile long stretch of mountains just west of Mexico City to the Great Lakes and back every year. Lincoln Brower, who is a leading expert on the monarch, has been studying the route of the monarch and the navigation techniques they must use to make their incredible journeys.
Brower has been able to show that most of the monarchs from Mexico make their way from Mexico to Texas and Louisiana where they lay their eggs and die. The first generation butterflies that hatch from these eggs reach the Great Lakes where they reproduce and die. Their offspring head east to the Appalachians and the East Coast and lay their eggs and die. Their offspring head south to the Gulf Coast, veer west and go back to Mexico, so it is the fourth generation of monarchs that complete the trip.
Notice that the monarch has made a giant circle as a group, with each generation flying in a place it has never been before. The evidence is that the navigation system that allows this is magnetically oriented. When the first group of monarchs begins the journey, the butterflies' magnetic compass, which seems to be crystals of magnetic material in their bodies, is pointed north. Every day, it turns about one degree clockwise so that, by the time the butterflies get to Texas or Louisiana, it is pointing northeast. Their offspring follow this northeast compass to the Great Lakes, but the compass they pass onto their offspring is set on east!
When the temperatures begin to cool and days get shorter, the compass is set on southeast, then south, and then southwest until they arrive back in Mexico. The one question Brower cannot answer is, "what sets the compass?" Is it temperature, length of day, or a genetic predisposition? This research has gone on for 40 years and has given us some incredible insights. We would suggest that the complexity of the system implies a design for survival given by God to enable this tropical butterfly to grace all of our country.
--Data from Discover, May, 1996, pages 89-139.