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Only 1,914 western monarchs observed at overwintering sites during the 2020 Thanksgiving Count

Jan 19, 2021


  • Population Trends

Today, our partners at the Xerces Society announced their final results from the Western Monarch Thanksgiving Count; only 1,914 overwintering monarchs were observed in the west in 2020. These are devastating, record-low numbers. The following summary is based on the Media Release and Blog Post released today by the Xerces Society, which we highly recommend you explore in more detail. 

The annual Western Monarch Thanksgiving Count organizes volunteers to observe and record the number of overwintering monarchs along the Pacific Coast of California down to northern Baja, Mexico. The western monarch population is one of only two migrating populations of monarch butterflies in the world; the eastern population migrates to central Mexico, while the western population overwinters in California. The 2020-2021 overwintering population numbers for eastern monarchs have not yet been released, but are usually available in March. 

The 2020 overwintering population of western monarchs is direly low. The total count of 1,914 monarchs represents a 99.9% decline in the population of migrating western monarchs since the 1980s. California overwintering groves were once covered in an estimated 4.5 million monarchs each winter. When the Western Monarch Thanksgiving Count started in 1997, over 1.2 million overwintering monarchs were observed at 101 sites. Even while implementing safety precautions amid the COVID-19 pandemic, volunteers were able to monitor a total of 246 sites in 2020 - three more sites than in 2019. To download an excel file of Western Monarch Thanksgiving Count data, please visit 

Xerces Society Western Monarch Thanksgiving Count. 2021. Western Monarch Thanksgiving Count Data, 1997-2020. Available at

With the current crisis for the western monarch population, the Monarch Joint Venture is committed to focusing our energies more strongly on habitat, science, education, and partnerships in the West in 2021 and beyond. To learn more about what you can do to support western monarchs, please read the Western Monarchs Call to Action

The Monarch Joint Venture is a 501c3 nonprofit organization and a national partnership of federal and state agencies, non-governmental organizations, businesses and academic programs working together to conserve the monarch butterfly migration. The content in this article does not necessarily reflect the positions of all Monarch Joint Venture partners. Header photo is of overwintering monarchs in California taken in 2013 by Wendy Caldwell.