BOB HIRSHON (host):
How monarch butterflies migrate. I’m Bob Hirshon and this is Science Update.
Every fall, monarch butterflies migrate from North America to a few parts of Mexico. It’s known that they use the sun as a compass. But it was also widely assumed that they have a mental map of their route, like homing pigeons.
HENRIK MOURITSEN (University of Oldenburg, Germany):
Normally, if you want to find a few kilometer-wide goal after 3 1/2 thousand kilometers, you have to have a map. But these guys don’t have a map. And that’s quite surprising.
That’s biologist Henrik Mouritsen of the University of Oldenburg in Germany. His team proved the butterflies rely on their compass alone, by moving a population from Ontario 1,500 miles west to Calgary. The relocated butterflies still tried to migrate southwest, which wasn’t the right direction anymore. Mourtisen says that normally, simply following the coastline helps the monarchs stay on track. I’m Bob Hirshon for AAAS, the Science Society.