Climate Change Threatens Monarchs
New research indicates that climate change could fracture the mass migration routes of monarch butterflies. Scientists found that suitable milkweed habitat, which is crucial for the butterflies' wintering period in Mexico, may shift further south. This change threatens to disrupt established migration patterns and could potentially lead some butterfly populations to remain in the north.
The eastern monarch butterfly population, which travels up to 3,000 miles, has experienced a dramatic 59% decrease in the area they occupy in their Mexican wintering grounds during the 2023-2024 season. This marks the second-smallest area recorded since monitoring began in 1993. The western monarch population, which migrates to coastal California, has seen an even more drastic short-term decline. The 2024 count tallied 233,394 butterflies, a number that, while higher than the near-extinction event of 2020, is still only 5% of the population numbers seen in the 1980s. A study by researchers from the National Autonomous University of Mexico projects that suitable habitat for monarch eggs and larvae in Mexico could shrink by 8% to 40% by the year 2070. This is due to the anticipated southward shift of milkweed, the exclusive food source for monarch caterpillars. This habitat fragmentation threatens to make the monarchs' journey more energetically demanding. Scientists suggest that some monarch populations may cease their long-distance travel and establish year-round breeding populations in central and northeastern Mexico as a result. The long-term sustainability of the eastern monarch population is considered to require a wintering area of at least six hectares. The 2023-2024 survey measured only 0.9 hectares, significantly below this threshold for a healthy population. Conservation efforts are now focused not just on protecting the wintering sites in the Monarch Butterfly Biosphere Reserve, a UNESCO World Heritage Site, but also on restoring milkweed and nectar plant corridors along the entire migration route.
