Climate change threatens monarch butterfly migration
New research indicates that climate change could severely disrupt the mass migration of monarch butterflies. Scientists found that suitable milkweed habitat, which is critical for the butterflies' survival in Mexico, may shift further south. This could fracture established migration routes and jeopardize the entire monarch population in North America.
The eastern migratory monarch population plummeted by 59% during the 2023-2024 winter season, occupying only 2.2 acres of forest in Mexico, the second-smallest area since monitoring began in 1993. This sharp decline is part of a longer trend that has seen the population decrease by more than 80% over the last three decades. In response to the drastic population drops, the migratory monarch butterfly is now classified as "Vulnerable" by the International Union for Conservation of Nature (IUCN). In December 2024, the U.S. Fish and Wildlife Service proposed listing the monarch as a threatened species under the Endangered Species Act. Canada has already designated the monarch as "Endangered" under its Species at Risk Act. The western monarch population, which migrates along the Pacific coast, is in even more dire straits, with a staggering 96% decline recorded in the 2024-2025 count. Researchers estimate that the western population has a 98% to 99% probability of extinction within the next 60 years if current trends continue. While climate change poses a significant threat, it is one of several factors driving the monarch's decline. The widespread use of herbicides, particularly glyphosate, has decimated milkweed, the only plant that monarch caterpillars can eat. Loss of overwintering forest habitat due to logging and development has also contributed to the population crash.
