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Searching for the Monarch’s Other Home

Monarch wings could answer the question: where are Western Monarchs born?


Every winter Western Monarch butterflies make their home on the Central Coast.  Come spring, no one knows exactly where they go.  Now researchers aim to find out the Monarchs' other home, where the next generation is born.    

Enter ecologist Louie Yang.  In his lab at UC Davis, a research assistant feeds tiny cylindrical tubes into a machine  about the size of a small microwave.  “It’s a grinder, it’s a magnetic grinder thing, she’s actually grinding Monarch wings,” said Yang.  Yang studies the Monarch butterfly. With one of his studies, he hopes to answer the question: Where do Monarchs go when they leave their winter homes along the California coast? To figure that out, Yang’s team gathered Monarchs from four sites along the coastline. “The Monarch wings are frozen in liquid nitrogen and then a magnetic impactor smashes them into a powder, and that powder is analyzed with a mass spectrometer,” said Yang.  The researchers analyze that powder to see how much hydrogen it contains, which tells them roughly where the butterfly was born.  "Water from rainfall contains both of these forms of hydrogen -- hydrogen and deuterium -- in a ratio that changes as rain clouds move over the continent, so on the coast there is a certain ratio of hydrogen to deuterium, but as precipitation moves further inland, that ratio changes.”  Yang says that ratio tells us a lot.“When we measure the hydrogen that is built into the wing of the Monarchs we can get a ratio of hydrogen to deuterium and then make some kind of guess as to where did that Monarch develop as a caterpillar,” said Yang.  If he can figure out where the butterflies are born, that’s information that conservationists are eager to have.


The Xerces Society, based in Portland, Oregon keeps count of the Monarchs that overwinter along the coast.  The numbers fluctuate from year to year, but the overall trend is down,  a steep 90 percent decline in the past 15 years.  To maintain or even boost the Monarch population, Xerces is leading a massive effort in the Western U.S. to plant milkweed.  It’s the only plant where Monarchs lay their eggs.  Xerces Executive Director Scott Black says Yang’s research will give them a better idea of where to plant the milkweed.  “Knowing where the butterflies are in the landscape and laying their eggs and where the young are feeding will allow us to do conservation of those areas and work with land managers and identify really important areas for Monarchs and try to make sure those areas are conserved,” said Black.  He says if conservationists are successful, “people would see more Monarchs. That is the goal. In the 90s and late 80s, there were hundreds of thousands of Monarchs at sites from Monterey down to Pismo Beach. Our goal is to not lose these populations, our goal is to allow these populations to persist over the long term so my kids who are 7 and 9 can go to these sites as adults and see Monarchs at Pacific Grove,” said Black.


Ecologist Louie Yang expects to answer the question, where are Western Monarchs born, in about six months. 

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