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Butterfly secret revealed

The monarch may rely on its biological clock to navigate its migration to Mexico.

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Somewhere over the Pacific Northwest this morning, a monarch butterfly is skipping uncertainly across the landscape. A few months ago, its grandparent left this misty stand of eucalyptus and cypress on the California coast some 700 miles away. By mid-autumn, its grandchild will begin the trip back, perhaps even to the same branch, to complete one of the most remarkable migrations in the animal kingdom.

For years, few answers have emerged as to how a creature that weighs less than a dime and has a brain smaller than a pin head could navigate its annual circuit with GPS precision.

Today, however, scientists say they have found their first big clue - evidence that monarchs rely on their biological clock to precisely chart the motion of the sun and calibrate their course.

More work remains, scientists say, before they can comprehend the migration entirely. But they hope this discovery will lead them to conclusions about an enigma that has long captured the imagination of backyard Darwins across North America.

"This is a really big step ahead in figuring out how monarchs find their way to [California and] Mexico and understanding such a complex process," says Lincoln Brower, a biologist at Sweet Briar College in Virginia.

In this week's issue of the journal Science, the authors of a new report suggest that monarch's circadian clock - the biological clock that sets sleep patterns in humans - is crucial to its ability to know where it is going. In other words, the monarch's clock inherently knows how to compensate for the hourly and daily movement of the sun across the sky, allowing the butterfly to fly in the exact direction it desires.

The study brings the way the circadian clock "tells an animal how to orient itself in space," says author Steven Reppert of the University of Massachusetts Medical School in Worcester. "It's like a four-dimensional clock."

What it does not answer is how monarchs know which direction they want to fly in the first place, and how they know when they have arrived at the exact wintering grounds in Mexico and coastal California that only their great-great grandparents saw.

It is a mystery that has given the monarch a unique niche in American culture, from nationwide counts of butterflies to migration maps pinned to cork boards in countless elementary schools.


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