Monarchs Take Generations to Make Annual South-North Journey

Citizen science data reveal how the declining species travels from its southern wintering site to its northern breeding grounds

Detail of graphic that shows number of recorded sightings of eastern monarch butterflies by latitude from May through July.

Katie Peek

Join Our Community of Science Lovers!


On supporting science journalism

If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.


It’s spring, and monarchs are on the move. Every year the butterflies leave their dense winter clusters near Mexico City and head for northern latitudes. It will take four months and three generations to get there. Once they arrive, the butterflies will get busy boosting their company enough to survive next year’s winter. It’s a Sisyphean task—eastern monarch numbers have dropped 80 percent in the past 20 years because of habitat degradation (including fewer flowers)—throughout their range, says Iman Momeni-Dehaghi, a biologist at Carleton University in Ottawa. Enter citizen scientists, who have been building databases such as Journey North, which Momeni-Dehaghi recently used to identify where the overwintering generation hatches. The data could help researchers devise more targeted interventions for a species in rapid decline.

Credit: Katie Peek; Sources: Monarch Sightings from Journey North Citizen Science Data (journeynorth.org); Population Data from Columbia University’s Socioeconomic Data and Applications Center (SEDAC)

Katie Peek is a science journalist and data-visualization designer with degrees in astrophysics and journalism. She is a contributing artist for Scientific American.

More by Katie Peek
Scientific American Magazine Vol 326 Issue 3This article was published with the title “The Great Monarch Odyssey” in Scientific American Magazine Vol. 326 No. 3 (), p. 84
doi:10.1038/scientificamerican0322-84

It’s Time to Stand Up for Science

If you enjoyed this article, I’d like to ask for your support. Scientific American has served as an advocate for science and industry for 180 years, and right now may be the most critical moment in that two-century history.

I’ve been a Scientific American subscriber since I was 12 years old, and it helped shape the way I look at the world. SciAm always educates and delights me, and inspires a sense of awe for our vast, beautiful universe. I hope it does that for you, too.

If you subscribe to Scientific American, you help ensure that our coverage is centered on meaningful research and discovery; that we have the resources to report on the decisions that threaten labs across the U.S.; and that we support both budding and working scientists at a time when the value of science itself too often goes unrecognized.

In return, you get essential news, captivating podcasts, brilliant infographics, can't-miss newsletters, must-watch videos, challenging games, and the science world's best writing and reporting. You can even gift someone a subscription.

There has never been a more important time for us to stand up and show why science matters. I hope you’ll support us in that mission.

Thank you,

David M. Ewalt, Editor in Chief, Scientific American

Subscribe