Monarch butterfly tracking could be done more effectively by mapping strontium isotopes

Researchers have shown through a new study that monarch butterflies can be effectively tracked along their migratory route by mapping strontium isotopes.

The study by University of Ottawa biology student Megan Reich sheds light on how mapping strontium isotopes can greatly improve the ability to track these important insects. Reich says that it is possible to combine strontium isotopes with hydrogen isotopes to pinpoint where a monarch butterfly hatched to a more precise area and can even be used to apply it to a sample of monarchs to see where they originated.

Monarch butterfly tracking over their migratory route that span thousands of miles is a complex and expensive task. Further, recovering tagged monarchs is rare and so gathering a complete understanding about these insects along their travel route is very difficult.

Understanding the migration routes of an insect that transports biomass, nutrients, pollen, genetic information, and ecosystem services across a continent is critical, especially to understand why this butterfly’s population numbers have been declining.

While technological advancement and deeper scientific understanding led scientists to use hydrogen isotopes for tracing the natal origin of monarch butterflies, the location was more general and spread over a vast area because hydrogen isotopes can only tell you the general area where the tissue was formed.

In this study researchers were able to show that strontium isotopes, particularly when combined with hydrogen isotopes, can help researchers pinpoint where a monarch butterfly hatched to a more precise area – about four times better.

Ultimately, Megan analyzed 100 monarch butterflies and found the overwintering monarchs likely originated in Texas, demonstrating the ability of isotopes to answer essential questions about animal migration, providing a geographic snapshot and potential clues to understanding population decline.

Megan adds that there are multiple reasons why monarch butterfly population is declining. Some of the major reasons include deforestation, extreme weather events, loss of habitat on the summer breeding grounds, mortality during the southward migration, increased parasitism, and the effects of climate change.

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