Climate Change Threatens Monarch Butterfly Migration
Climate change may significantly disrupt the mass migration of monarch butterflies, according to a new analysis. Rising temperatures are projected to shift essential milkweed habitats in Mexico southward. This change could fracture traditional migration routes, threatening the monarch population and the broader ecosystems that rely on them as pollinators.
The migratory monarch butterfly is now classified as vulnerable by the International Union for Conservation of Nature, with its populations having declined by over 80% in central Mexico and over 95% in California since the 1980s. In December 2024, the U.S. Fish and Wildlife Service proposed listing the monarch as threatened under the Endangered Species Act, a step already taken by Canada in 2023. A key threat is the loss of milkweed, the only plant monarch caterpillars eat. The expansion of herbicide-resistant crops in the Midwest has decimated milkweed patches that once grew between rows of corn and soybeans. This loss of breeding habitat is compounded by the degradation of overwintering forests in Mexico due to logging and agriculture. The analysis highlighted in the news card was published in the journal *PLOS Climate* by researchers at the National Autonomous University of Mexico. Using computer modeling, the study projected that by 2070, the changing climate could reduce suitable monarch habitat in Mexico by between 8% and 40%. This habitat shift poses a serious threat to the migration itself. The southward movement of milkweed could concentrate egg-laying sites farther from the U.S. border, making the journey more demanding and potentially causing some monarchs to establish non-migratory resident populations in central Mexico. Beyond habitat shifts, climate change brings other dangers. Warmer autumns can delay the departure for migration, leading to butterflies dying in the cold before reaching their destination. More frequent and intense storms also pose a direct threat; a single storm in 2002 killed an estimated 80% of the overwintering population in Mexico. Conservation efforts are underway, involving multiple countries and organizations. In Mexico, the Monarch Butterfly Biosphere Reserve is a protected UNESCO World Heritage Site. In the U.S., organizations like the National Wildlife Federation are working with mayors and communities to create new monarch habitats by planting milkweed and nectar-rich wildflowers in urban and suburban areas.
