Monarch butterflies are famous for their long migrations, typically overwintering in the mountains of central Mexico and migrating to eastern North America during the warmer months. However, in recent years fewer monarchs have been are reaching their overwintering sites and scientists haven’t been able to determine why. New research published in De Gruyter's Open Access journal Animal Migration intends to shed light on this migration conundrum.
While previous theories regarding the decreasing population of monarchs in central Mexico during overwintering months point towards the dangers of the long migration or say the decline reflects a falling number of breeding adults, this new study suggests another cause: perhaps monarchs are overwintering in different places.
Dr. Hannah Vander Zanden, from the University of Florida, who led the study titled, "Alternate migration strategies of eastern monarch butterflies revealed by stable isotopes”, says her team’s research suggests that monarchs may be migrating to new locations, such as coastal southern Florida.
Andy Davis, the editor of the journal and an expert in monarch migration, commented that "Previous research had suggested that some migrating monarchs may wind up in southern Florida if they become waylaid by strong westerly winds, but this evidence makes it seem like they purposely traveled to this location."
Dr. Vander Zanden utilized a technique to analyze monarchs that she and her team captured and examined in South Florida. They were able to sample the insects’ body or wing tissues to determine the butterflies’ migration patterns and figure out where they came from. What they found was shocking: half of the monarchs came from the American Midwest, “which is typically thought to represent the core breeding range of the eastern population,” reports Science Daily. Historically, scientists have thought that this monarch population only overwintered in central Mexico. But, clearly, that is not the whole picture.
This research was published along with four other studies concentrating on monarch migration. Davis commented, "Collectively, these studies demonstrate that we still have so much to learn about this phase of the monarch life cycle in North America. And, given the issues facing the migration itself, this work couldn't come at a better time.”