Newsroom Midwest Region

Solving monarch birth mysteries

March 15, 2017

Monarch caterpillar four days after hatching by Joanna Gilkeson/USFWS.
Monarch caterpillar four days after hatching by Joanna Gilkeson/USFWS.

Did you know that the wings of a monarch hold a secret? One of the greatest puzzles in ecology is the mystery of migration, and it is in the process of being solved for monarch butterflies. The milkweed leaves that caterpillars eat contains a distinct chemical signature from the soil and water that is absorbed into the plant, and ultimately into the monarch's wings as they develop into adult butterflies. By analyzing their wings, scientists can map where butterflies found in Mexico were born.

A recently published study (Flockhart et al. 2017) provides another layer of data to our understanding of the monarch migration phenomenon. By analyzing stable hydrogen and carbon isotopes (similar to fingerprints) and geospatial modeling, researchers were able to more accurately pinpoint where the monarchs that overwinter in Mexico are born. The researchers collected more than 1,000 monarchs from the overwintering sites in Mexico from 1976 to 2014. The butterfly samples show different levels of these stable isotopes; by comparing these levels to known geographic variation, they have estimated the birthplace of each butterfly.

Key findings of the study are:

  1. The Midwest is still the primary contributor, but the contribution may be smaller than previously thought
  2. Monarch origins have not shifted over time due to habitat loss
  3. Climate patterns influence the proportion of monarchs from different regions

These results suggest that monarch conservation must encompass all areas of the eastern breeding grounds to ensure a future filled with monarchs.

Even better news is that we are working with the researchers on the next two phases for this study to increase the precision of mapping monarch origins. Currently, isotope data is being analyzed for several hundred samples that were collected in 2016. We hope that “phase two” of this study will provide an understanding of different mortality patterns by comparing isotopes of butterflies that survive the winter and those butterflies that did not survive the winter, which may be a product of where they are born and their sex.

For “phase three” of the study we hope to increase the precision of monarch origins for producing a more accurate base map. This phase is investigating the use of another isotope called strontium. Strontium isotopes have been used for analysis of bird feathers, bat hair and fish bones.

"We always want to use the best science available,” says Craig Czarnecki, U.S. Fish and Wildlife Service Midwest Assistant Regional Director for Science Applications. "Using isotopes offers helpful insights into the ecology of monarch migration."

As additional pieces are added to the monarch’s migration puzzle, it’s clear that everyone can help with monarch and pollinator conservation, no matter where you are on the map.

Monarch conservation must be conducted in all areas of the eastern breeding grounds to ensure a future filled with monarchs. Graphic courtesy of KAP Design.
Monarch conservation must be conducted in all areas of the eastern breeding grounds to ensure a future filled with monarchs.
Graphic courtesy of KAP Design.

 

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