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Environment

MSU Research Team Links Climate Change With Decreasing Eastern Monarch Butterfly Populations

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Michigan State University ecologists collaborated internationally with both professional and volunteer scientists to better understand what is driving a decline of Eastern monarch butterflies.

The steepest decrease was observed in the mid-1990s to mid-2000s, when glyphosate weed killers became widely popular within the agriculture industry. Those chemicals killed milkweed plants which are the sole host and food source for monarch caterpillars.

But the team found climate change has had the most significant impact on the population in recent years.

Researchers found when the weather was extreme or well above normal in the butterflies’ spring and summer breeding grounds in the southern United States, population sizes were smaller.

Erin Zylstra is the study’s lead author. She says normal warm temperatures promote fast development of caterpillars, but extreme heat can impact how the adult butterflies reproduce.

Her team recorded precipitation amounts and temperatures in Eastern Texas and analyzed climate data in the Midwestern United States and Southern Ontario.

"We can sort of link those up with what the survey data tells us about monarchs during that year and in that area, and so we were able to use that to sort of say 'Okay, when temperatures are well above normal, we have lower counts of monarchs generally in those areas.'"

MSU Associate Professor of Integrative Biology, Elise Zipkin says the next step is to predict what areas, as the climate changes, would be better suited for monarch butterflies, so researchers can target conservation efforts.

"We care. We want to figure out what’s going on, but we also care about providing solutions to these sorts of big grand challenges."

The butterflies migrate between Mexico and the eastern half of the U.S. and southern Canada every year — including summer layovers in Michigan as well as other states.

McKoy's story is brought to you as part of a partnership between WKAR and Michigan State University's Knight Center for Environmental Journalism.

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