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What Scientists Say
About the Navigation Puzzle

Magnetic Cues?
"Scientists have suggested that monarchs may use a magnetic compass to orient, as has been demonstrated in some migratory birds. However, Mouritsen and Frost (2002) showed that migratory monarchs . . . did not respond to magnetic field shifts, suggesting that monarchs do not use the earth’s magnetic field to orient during migration."
— Ecology Online Sweden

Listen! Study Sheds Light on Monarch Migration (radio clip)
Still a Puzzle
“It is annoying that the press implies the problem has been solved. “The findings do not suggest a navigational mechanism by which monarchs from the eastern two thirds of North America can find 13 or so small areas in the Transvolcanic Belt of Michoacan. Using a sun compass can lead (orient) monarchs in a general direction with respect to the sun. But this mechanism alone will not get them to Michoacan. Since the sun is constantly changing its position in the sky, monarchs must and apparently can compensate for the changing position of the sun.
— Dr. Bill Calvert, monarch biologist

Dig Deeper: Learn how scientists confirmed this theory about monarch navigation systems: How Do Monarchs Know Which Way to Fly?
Sun Compass
"Monarchs may use the angle of the sun along the horizon in combination with an internal body clock to maintain a southwesterly flight path. For example, if a monarch’s internal clock reads 10:00 am, then the monarch will fly to the west of the sun to maintain a southern flight direction. When the monarch’s internal clock reads noon (12:00 pm), the monarch’s instincts tell it to fly straight toward the sun, while later in the day the monarch’s instincts tell it to fly to the east of the sun.

[But] if all the monarchs in eastern and central North America maintained a southwesterly flight, they could never all end up in the same place. It has been proposed that mountain ranges are important landmarks used by monarchs during their migration."
— Dr. Karen Oberhauser, Monarch Lab

More Mystery
“If monarchs just used the sun to orient south, few would make it to Mexico since most would end up in the Gulf of Mexico. Although the papers on sun compass orientation are valuable contributions toward our understanding of the monarch migration, how monarchs set their bearing remains a mystery and the one that needs to be solved before we fully understand how they navigate during the migration."
— Dr. Chip Taylor, Monarch Watch

New Research: Brains and Eyes Combine (August 2005)
Light in general is essential to the functioning of the "biological clock" in the butterfly brain – governing . . . its "signal" to migrate. But the researchers discovered that it is specifically the ultraviolet (UV) band of light [which humans can't detect] that is crucial to the creature's orientation. The butterflies have special photoreceptors for UV light in their eyes.

They proved that this ultraviolet "navigation" is crucial by placing butterflies in a "flight" simulator. When a UV light filter was used in the simulator, the butterflies lost their orientation.

Further probing revealed a key wiring connection between the light-detecting navigation sensors in the butterfly's eye and its brain clock. Thus, it was shown that input from two interconnected systems – UV light detection in the eye and the biological clock in the brain – together guide the butterflies "straight and true" to their destination.
— From press release, The Hebrew University of Jerusalem

Geographic Cues
"I personally think that the Mexican mountains focus the migration once the butterflies enter Mexico."
— Dr. Bill Calvert, monarch biologist
(More of Bill's comments on Monarch Orientation Mechanisms)

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