From the Archives: Monarch Butterflies Declining Faster than Previously Thought

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Monarch butterflies are famous for their annual migration from southern Mexico to the eastern United States, which is one of the world’s most complex insect migrations. The Eastern Monarch butterfly population has been declining for decades, and a 2015 SESYNC paper demonstrated that the rate of decline had increased to six times the previous rate since 2008. The lead author, Leslie Ries, was a SESYNC-supported researcher who led synthesis teams through a Workshop and Venture. The team mobilized citizen science data to compare winter and summer monarch populations and document the steep rate of decline. 

Monarch butterflies have been well-monitored in their Mexican overwintering sites, where it is easier to estimate the population’s total size. It has been harder to estimate populations at the summer breeding grounds in the US because the butterflies spread across a much larger geographic area during this time. This SESYNC study was the first to attempt a comprehensive analysis that included most of the monarch’s primary breeding grounds. The researchers relied on citizen science data gathered by groups such as the North American Butterfly Association. Using this data, they found less evidence for decline in the summer populations than the winter ones but noted that further analysis of the summer populations would help elucidate major factors driving the overall population decline. 

In addition to publishing papers describing these patterns, members of the research team went on to develop a tool called PollardBase, which will help facilitate additional cross-site analyses. PollardBase is a website that manages data from volunteer monitoring efforts across the country, making citizen science data more accessible. The researchers also made a point of visiting volunteer monitoring workshops, where citizen scientists learned how the data they collected was being used. 

This post is adapted from a 2015 SESYNC news item. This is part of our ongoing series to share our most popular stories from the SESYNC research archives.