MEXICO CITY — This year saw a significant revival in the number of monarch butterflies hibernating in the mountainous regions west of Mexico City. The area covered by these vibrant insects doubled in 2024, despite ongoing challenges from climate change and habitat degradation, experts reported on Thursday.
Rather than counting each individual butterfly, the annual survey measures the acreage occupied by the monarchs as they cluster together on the branches of pine and fir trees in these high-altitude forests. These butterflies make their journey from regions east of the Rocky Mountains in the United States and Canada to overwinter in Mexico.
The Mexican government’s Commission for National Protected Areas (CONANP) announced that this year’s butterfly gatherings spanned 4.4 acres (1.79 hectares), a stark improvement from the mere 2.2 acres (0.9 hectares) recorded the previous year. Last year’s count had marked a 59% decline from 2023, ranking it as the second lowest since records began.
Once winter concludes in Mexico, these striking orange and black butterflies commence their northward migration. As they journey towards southern Canada, they breed successive generations, ultimately setting the stage for a return migration to Mexico by late summer.
According to Gloria Tavera Alonso, Director General of Conservation for the Mexican agency, the healthier butterfly numbers this season are a result of improved weather patterns and increased humidity. In the previous year, drought along their migratory path significantly contributed to the dwindling numbers.
The dynamics of annual weather variations and their resultant impacts on butterfly populations indicate that continual fluctuations should be anticipated. Jorge Rickards, Mexico’s Director General for the World Wildlife Fund, emphasized the importance of relentless conservation efforts to safeguard these creatures’ future.
Efforts to bolster the availability of vital plants that sustain and support monarch butterfly reproduction during their migration have been credited as a significant factor in their recovery.
Outside Mexican borders, monarch butterflies have faced severe challenges. The Xerces Society for Invertebrate Conservation has monitored the western populations of monarchs—distinct from those wintering in central Mexico—along California’s coast, northern Baja California, and inland California and Arizona for nearly three decades. In stark contrast to the 1.2 million butterflies observed in 1997, this year’s analysis revealed just 9,119 individuals in 2024, showing a staggering 96% drop from 233,394 recorded in 2023. This tally is the second lowest since surveys began in 1997.
A recent comprehensive analysis has also detailed the decline in butterfly populations across the contiguous United States. The study found an average annual decrease of 1.3% in butterfly numbers since the start of the 21st century. Among the 114 declining species, only a handful showed increases, as published in the journal Science.
Experts have highlighted that monarch butterflies face numerous threats throughout North America, primarily stemming from the loss of milkweed, essential for laying eggs. This vital plant is vanishing due to a combination of drought, wildfires, urban sprawl, and the use of herbicides.
In response, the U.S. Fish and Wildlife Service proposed extending protection to monarch butterflies under the Endangered Species Act, classifying them as a threatened species.
