Climate Change Threatens Monarch Butterfly Migration
New scientific research indicates that climate change is imperiling the mass migration of monarch butterflies. Shifting environmental conditions are forecast to push suitable milkweed habitats further south in Mexico, which could fracture established migration routes and threaten the survival of some monarch populations.
The eastern monarch population, known for its 3,000-mile migration, has plummeted by over 80% since the 1990s. The western population, which overwinters in California, has fared even worse, declining by more than 95% since the 1980s. During the 2023-2024 winter season, the eastern monarch population occupied only 2.2 acres in Mexico, a 59% decrease from the previous year and the second-smallest area ever recorded. Warmer autumns are causing some monarchs to begin their migration up to six weeks late, leading many to perish in the cold. Climate models predict that the traditional overwintering grounds in Mexico's mountains may soon become unsuitable. This forces the butterflies to find new winter habitats, potentially in the southern U.S., where they would face different and colder conditions. Monarchs are highly sensitive to temperature, which provides environmental cues for reproduction, hibernation, and migration. Rising temperatures can disrupt these signals; if it's too warm, butterflies may not receive the prompt to start their northward flight in the spring. Conversely, an abundance of milkweed and warm temperatures in the fall can prevent them from leaving for their overwintering grounds. The butterflies' survival is inextricably linked to milkweed, the sole host plant for their eggs and food for their caterpillars. Climate change-induced high temperatures and drought have reduced the availability of this vital plant. Furthermore, the widespread use of herbicides, particularly glyphosate on genetically modified crops, has been a primary driver of milkweed loss along migration routes. Conservation efforts are underway across North America. The U.S. Fish and Wildlife Service has proposed listing the monarch as a threatened species under the Endangered Species Act. In Canada, monarchs were listed as endangered in 2023, and their overwintering sites in Mexico are legally protected within the Monarch Butterfly Biosphere Reserve. Organizations like the National Wildlife Federation and the Xerces Society are working to restore monarch habitat by planting native milkweed and creating conservation networks. The Monarch Butterfly and Pollinators Conservation Fund has awarded over $31 million to 165 projects since 2015, supporting the restoration of 430,000 acres and the propagation of 1.2 million milkweed seedlings.
