The World Wildlife Fund–Mexico announced yesterday results of the annual survey of monarch butterflies overwintering in central Mexico. The butterflies occupied an estimated 2.1 hectares of forest during the winter of 2020–21. This was a reduction of approximately 26% compared to the previous winter, when monarchs occupied 2.83 hectares. Scientists estimate that 6 hectares are necessary to sustain the population.
Monarchs at the El Rosario reserve in early 2018. (Photo: Xerces Society / Candace Fallon.)
Combined with the results from Xerces Society’s Western Monarch Thanksgiving Count of butterflies overwintering along the California coast, this underscores that monarchs are not recovering and still urgently need extraordinary conservation efforts throughout North America. Climate change, pesticide use, and habitat loss in both Mexico and the U.S. threaten the eastern monarch population (which overwinters in Mexico) and the western population (which primarily overwinters in California).
The Xerces Society will continue to pursue protection for the monarch and will maintain and expand our efforts to protect, restore, and create habitat across the country.
Press Release from WWF–Mexico
Results from surveys of overwintering monarchs in Mexico, 2020–21 season (WWF–Mexico) [Spanish language]
Report from WWF–Mexico on changes to forest cover in the core area of the Monarch Butterfly Biosphere Reserve (2019–20) [Spanish language]
Xerces Society’s Western Monarch Call-to-Action
More articles about monarchs on the Xerces blog