Monarch Butterfly Migration

MONARCHS – Internal CompassHere’s a program from our archives. Around this time of year, Monarch butterflies will begin migrating northward from the forests of Mexico where they’ve spent the winter. The question is, how do they know where they’re going? I’m Jim Metzner, and this is the Pulse of the Planet.Brower: The monarch has the most complicated migration of any insect known. It’s a completely inherited, highly specific behavior that is unique to the Monarch butterfly.Lincoln Brower is a Research Professor of Biology at Sweet Briar College. He tells us that it takes five generations of Monarch butterflies to complete the annual migration cycle between Mexico and the Northern United States. And yet, late each fall, a group of young butterflies returns to the same patch of Mexican forest where their great grandparents spent the previous winter. And the mystery is, how do they find their way?Brower: They’re following some kind of a compass. And it’s known that the bodies of many insects, including Monarchs, have a magnetic mineral in their bodies. And it’s possible that that is like a compass and that they are setting a direction. But something has to change the direction, because in the fall they’re going south and in the spring they’re going north. And so that compass is not a constant; it’s changing throughout the life of the butterfly, which is why I generated this hypothesis that Monarch butterflies are really migratory throughout their entire lifetime and that they change their angle of migration direction one degree per day. They’re just changing their direction in a big circle, in the course of three hundred and sixty days.Experiments done on the Monarchs still haven’t uncovered all the secrets of the Monarch’s migration. Additional funding for this series has been provided by the National Science Foundation. I’m Jim Metzner.

Monarch Butterfly Migration

How do young Monarch butterflies find their way to their winter migration sites in the Mexican forest?
Air Date:03/15/1999
Scientist:
Transcript:

MONARCHS - Internal CompassHere's a program from our archives. Around this time of year, Monarch butterflies will begin migrating northward from the forests of Mexico where they've spent the winter. The question is, how do they know where they're going? I'm Jim Metzner, and this is the Pulse of the Planet.Brower: The monarch has the most complicated migration of any insect known. It's a completely inherited, highly specific behavior that is unique to the Monarch butterfly.Lincoln Brower is a Research Professor of Biology at Sweet Briar College. He tells us that it takes five generations of Monarch butterflies to complete the annual migration cycle between Mexico and the Northern United States. And yet, late each fall, a group of young butterflies returns to the same patch of Mexican forest where their great grandparents spent the previous winter. And the mystery is, how do they find their way?Brower: They're following some kind of a compass. And it's known that the bodies of many insects, including Monarchs, have a magnetic mineral in their bodies. And it's possible that that is like a compass and that they are setting a direction. But something has to change the direction, because in the fall they're going south and in the spring they're going north. And so that compass is not a constant; it's changing throughout the life of the butterfly, which is why I generated this hypothesis that Monarch butterflies are really migratory throughout their entire lifetime and that they change their angle of migration direction one degree per day. They're just changing their direction in a big circle, in the course of three hundred and sixty days.Experiments done on the Monarchs still haven't uncovered all the secrets of the Monarch's migration. Additional funding for this series has been provided by the National Science Foundation. I'm Jim Metzner.