Continental breeding hotspots of migratory monarch butterflies revealed by coordinated community science partnership

Jayme M.M. Lewthwaite, André-Philipp Drapeau Picard, Guillaume Blanchet, Jens Ulrich, Vincent K. Fyson, Greg W. Mitchell, Carmen Galán Acedo, Julia Meyer, Heather M. Kharouba, Cuauhtémoc Cuauhtémoc, Jennifer Thieme, Commission for Environmental Cooperation (CEC), Maxim Larrivée, Federico Riva

The eastern migratory monarch butterfly (Danaus plexippus plexippus) has declined by more than 80% over the past two decades, highlighting the need for improved understanding of its breeding ecology. To address longstanding gaps in continental-scale data on monarch reproduction, the International Monarch Monitoring Blitz has mobilized community scientists across North America to monitor monarch reproduction. Using a hierarchical generalized linear model based on thousands of observations of larval density on milkweed across North America, we identified monarch butterfly mid-summer breeding hotspots. Our model suggests that such hotspots are broadly concentrated in the northeastern United States and southeastern Canada. Larval density was structured across multiple spatial scales, suggesting both local habitat conditions and broader regional factors contribute to variation. Our results demonstrate the power of coordinated community science to reveal large-scale ecological patterns and provide actionable information for monarch conservation across its breeding range.