Tagging Monarchs Helps Scientists Understand Their Migration

The paths of monarch migration have been discovered by tagging

Tagging Monarchs Helps Scientists Understand Their Migration

Thu, 2012-09-20

Monarch butterflies have a relatively short lifespan. Every winter, the monarchs travel from Canada to Mexico. When the weather warms up again, the butterflies in Mexico travel back north. The oldest butterflies live six to nine months, meaning they only make the return trip about halfway. 

Imagine a monarch that has traveled the 3,000 from Canada to Mexico, and then only makes it to Texas on the return journey. Say she lays an egg there, and that egg born in Texas births a monarch that flies to South Dakota and lays another egg. That monarch hatches, and manages to find her way to Mexico come autumn. How did the monarch travel to the exact same grove in Mexico that her elder monarchs did? 

Some animals that migrate learn from parents. Other creatures orient by stars or landmarks. How do monarchs know where to migrate south? Scientists are still trying to find out.

Dr. Orley R. Taylor, a scientist who runs the Monarch Watch project at the University of Kansas, has studied this mystery. He has tested their ability to reorient themselves. He transported monarchs from Kansas to Washington, D.C. to see if they could still successfully navigate after a relocation of more than 1000 miles. If the monarchs are released immediately after being relocated, they take off due south as they would have from their original location. However, if they are kept in mesh cages for a few days, they watch the sun rise and set, and reset their internal compasses. 

Dr. Taylor cites that monarchs are one of the only species that have the ability to orient themselves in latitude and longitude. When the sun drops to approximately 57 degrees above the southern horizon at their specific latitude, monarchs begin their migration.

Professor of neuroscience at Queens University of Canada Dr. Barrie Frost does not believe monarchs use the earth’s magnetic field or the sky’s polarized light. Rather, he thinks the sun reckoning leads the butterflies south, while mountain chains and the Gulf of Mexico funnel them towards southern Texas. Dr. Frost also believes that once in Mexico’s mountains, they are guided by the smell of last year’s corpses. 

Dr. Taylor disagrees, citing that butterflies do not have odiferous fatty acids that would last a year and lead a new migration herd. Citing work by butterfly biologist William H. Calvert, Dr. Taylor says most monarchs cross central Texas. Dr. Taylor’s tagging work has also shown that a monarch tagged near the Atlantic or the gulf is just one-tenth as likely to reach Mexico as one tagged in the Great Plains.

How do you tag a small, delicate monarch? Dr. Taylor will gently pinch the butterfly in one hand, and place a tiny adhesive tag on a specific cell. He is then able to track the butterfly for the entirety of its life, and uses these tags to follow the annual migration.