Climate Change Threatens Monarch Migration
The mass migration of monarch butterflies is at risk from climate change, according to a new scientific report. Researchers warn that rising temperatures may shift the location of suitable milkweed habitats in Mexico, which are critical for the butterflies' overwintering. This habitat shift could fracture existing migration routes and threaten the species' survival.
The recent study in *PLOS Climate* by researchers at the National Autonomous University of Mexico predicts that by 2070, suitable habitat for monarch eggs and caterpillars in Mexico could shrink by 8% to 40%. This southern shift in their breeding grounds could make the migration energetically more demanding for the butterflies. This isn't just a future problem. The eastern monarch population, which migrates from the U.S. and Canada to Mexico, has declined by over 80% since the 1990s. The western population, overwintering in California, has seen an even more drastic drop of over 95% since the 1980s. In 2020, fewer than 2,000 western monarchs were counted in California. Beyond the shrinking and shifting of milkweed habitats, climate change brings other threats. Increased frequency of extreme weather events like droughts and severe storms can be devastating. Warmer winters can also disrupt their hibernation state, known as diapause, causing them to burn through energy reserves needed for the spring migration north. Herbicides and pesticides are also major contributors to the decline. The widespread use of glyphosate-resistant crops has led to a massive loss of milkweed, the only plant monarch caterpillars can eat. It's estimated that over 850 million milkweed plants have been lost since 1999 due to herbicide use on croplands. In response to the declining numbers, conservation efforts are underway. In December 2024, the U.S. Fish and Wildlife Service proposed listing the monarch butterfly as a threatened species under the Endangered Species Act. Canada listed the monarch as endangered in 2023, and Mexico provides legal protection within the Monarch Butterfly Biosphere Reserve. Organizations and individuals are also taking action. The Xerces Society's Western Monarch Count engages citizen scientists to track population numbers. Efforts to restore milkweed and nectar sources are being promoted through programs like Monarch Watch's "Monarch Waystations," which encourages the creation of habitats in gardens, schools, and other unused plots of land.
