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Monarchs Overwintering in Mexico Down 53%

By Sarina Jepsen and Emma Pelton on 13. March 2020
Sarina Jepsen and Emma Pelton

Monarchs still urgently need Endangered Species Act protection in the United States and extraordinary conservation efforts throughout North America.

The World Wildlife Fund-Mexico and the Comisión Nacional de Áreas Naturales Protegidas (CONANP) announced today that monarchs in central Mexico occupied an estimated 2.83 hectares of forest during the winter of 2019-2020—a reduction of approximately 53% compared to last year, when monarchs occupied 6.05 hectares. Read more in English here, and in Spanish here.


Monarchs stand close together on muddy ground on the edge of a puddle.
In March 2018, this group of monarchs was observed "puddling" (drinking water from a small pool) in El Rosario, a section of el Reserva de Biosfera de la Mariposa Monarca, a World Heritage Site in the states of Michoacán and Mexico. Unfortunately, overwintering numbers are lower now. (Photo: Xerces Society / Candace Fallon)


It is clear from this announcement that monarchs are not recovering and still urgently need Endangered Species Act (ESA) protection in the United States and extraordinary conservation efforts throughout their range. Climate change, pesticide use, and habitat loss in both Mexico and the US continue largely unabated, and threaten both the eastern monarch population (which overwinters in Mexico) and the western population (which primarily overwinters in California).

The western population, whose numbers were reported recently, remains critically imperiled. This season’s Xerces Society’s Western Monarch Thanksgiving Count  and New Year’s Count have revealed that the migratory monarch population which breeds west of the Rocky mountains continues to hover at less than 1% of its historic population size for a second year in a row, whereas this year’s eastern population represents approximately one-third of its historic size.


Bright orange monarchs cluster together on a deep green pine branch.
The work to recover monarchs is far from over. Though some overwintering sites still look like this one viewed in 2018, the overall overwintering population in Mexico is down 53% from last year, and comprises two-thirds of historic levels. (Photo: Xerces Society / Candace Fallon)


The US Fish and Wildlife Service will make a decision about whether to list monarchs under the ESA in December 2020. The best science recommends the eastern population needs to sustain an overwintering size greater than 6 hectares over many years. Clearly, the work to recover monarchs is far from over.

To restore monarch populations across North America and ensure these butterflies’ incredible migration continues, everyone can help make a difference. We recommend creating and protecting habitat, reducing or eliminating pesticide use, contributing to community science projects, and supporting other monarch conservation efforts.

At Xerces, we work with farmers, roadside managers, and communities across the US to protect, restore and manage habitat for monarchs. We have restored over a million acres for pollinators, including monarchs, at sites across the US. We also focus on the protection and restoration of overwintering sites in California and their migratory and breeding areas across the West.


Further Reading

Learn more about our work and how to help monarchs here.

Learn about the work being done by our staff and partners at the USDA Natural Resources Conservation Service.

Check out the work of our partners at Journey North and Monarch Joint Venture.

To support monarchs in the West (west of the Rocky Mountains), please see



As the Xerces Society's western monarch lead, Emma works on the western population of monarch butterflies, including adaptive management of overwintering habitat in California and breeding habitat throughout the western U.S. Emma completed a master's degree in agroecology and entomology at the University of Wisconsin–Madison where her research focused on landscape ecology and an invasive fly that affects fruit crops.

Sarina directs the Xerces Society’s Endangered Species and Aquatic Program. Since joining the Society in 2006, Sarina has worked on the conservation of diverse at-risk North American invertebrate species, including bees, butterflies, beetles, and freshwater mussels. Sarina has authored multiple publications on the conservation of endangered pollinators and other at-risk species, and developed management guidance for federal agencies, such as the U.S. Forest Service, Bureau of Land Management, and Fish and Wildlife Service.

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