The number of monarch butterflies wintering in the mountains west of Mexico City, rebounded this year, doubling the area they covered in 2024 despite the stresses of climate change
Monarch Butterfly Numbers Rebound in Mexico, But Threats Persist
MEXICO CITY (AP) — Monarch butterflies wintering in the mountains west of Mexico City showed signs of recovery this year, doubling the area they covered in 2024 despite ongoing challenges from climate change and habitat loss, experts reported Thursday.
Rather than counting individual butterflies, the annual survey measures the area occupied by the butterflies as they cluster on tree branches in the mountain pine and fir forests. These monarchs, migrating from the United States and Canada, overwinter in these forests.
According to Mexico’s Commission for National Protected Areas (CONANP), the butterflies this year covered 4.4 acres (1.79 hectares), a significant increase from the 2.2 acres (0.9 hectares) occupied in 2023. Last year’s figure had marked a dramatic 59% decline from 2022, which was the second-lowest level recorded since monitoring began.
Once they leave Mexico in the spring, the iconic butterflies with black-and-orange wings fly north, breeding multiple generations as they travel thousands of miles. The last generation, which reaches southern Canada, begins its return journey to Mexico at the end of summer.
Gloria Tavera Alonso, director general of conservation at CONANP, attributed the improved numbers to favorable climatic conditions and better humidity. Last year’s drop was largely attributed to droughts along the butterflies’ migratory route.
Despite the positive turn this year, fluctuations in butterfly numbers are expected due to variable weather patterns, making it critical to remain vigilant, said Jorge Rickards, director general for the World Wildlife Fund (WWF) Mexico. He emphasized the need for continued conservation efforts.
Tavera Alonso also highlighted efforts to increase the availability of plants along the butterflies’ migratory path, essential for their sustenance and reproduction.
However, butterflies have not fared as well to the north.
The Xerces Society for Invertebrate Conservation has been monitoring western monarch populations in California, northern Baja California, and parts of Arizona for 28 years. The peak count was 1.2 million butterflies in 1997, but the 2024 count was just 9,119, a staggering 96% decrease from 233,394 in 2023. This marked the second-lowest count in the society’s records.
In addition, a comprehensive study of butterfly populations in the Lower 48 U.S. states found that the number of butterflies has been declining by an average of 1.3% annually since the turn of the century. The study, published in Science, noted that 114 butterfly species are significantly declining, while only nine have shown population increases.
Experts stress that one of the primary threats to monarch butterflies across North America is the dramatic loss of milkweed, the plant where monarchs lay their eggs. Milkweed has been disappearing due to a combination of drought, wildfires, herbicides, and urban development.