The population of monarch butterflies wintering in the mountains west of Mexico City has increased significantly, doubling its size in 2024. Experts say this recovery occurred despite ongoing threats like climate change and habitat destruction. Instead of counting individual butterflies, researchers measure the area they occupy as they cluster on tree branches in pine and fir forests. Monarchs from the eastern U.S. and Canada migrate to Mexico for the winter. Mexico’s Commission for National Protected Areas (CONANP) reported that the butterflies covered 4.4 acres (1.79 hectares) this year, up from 2.2 acres (0.9 hectares) in 2023, which had marked a steep 59% decline from the previous year. Favorable environmental conditions, such as humidity and temperature, contributed to this increase.

Monarch butterflies travel thousands of miles, with multiple generations born along the way before reaching Canada. At summer’s end, the final generation migrates back to Mexico. Conservation efforts focus on restoring native plants essential for food and reproduction. However, monarch populations in other regions are still declining. The Xerces Society for Invertebrate Conservation recorded only 9,119 western monarchs in 2024, a dramatic 96% drop from 233,394 the previous year. The main threats are habitat loss, urban expansion, and a decline in milkweed plants. Because of these risks, the U.S. Fish and Wildlife Service has proposed protecting monarchs under the Endangered Species Act.