Skip to main content

Monarch Numbers from Mexico Point to Declining Population

By Stephanie McKnight on 26. February 2021
Stephanie McKnight

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.


Orange-and-black monarch butterflies cling to the green branches of tress and fly in the blue sky
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.


Bar chart showing changes in the area covered by colonies of monarch butterflies in Mexico overwintering sites


Further Reading

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


Your Support Makes a Difference!

Xerces’ conservation work is powered by our donors. Your tax-deductible donation will help us to protect the life that sustains us.