Number of Monarch butterflies overwintering in California holds steady, but still well below the 1990s

Data released today show that more monarch butterflies were counted at overwintering sites in California this year compared to last year. While this is welcome news, the number of butterflies is still well below peak numbers from the 1990s. Volunteers with the Western Monarch Thanksgiving Count visited 162 sites in coastal California and tallied a total of 211,275 monarchs.

Monarch butterflies spend the winter in spectacular clusters in the Oyamel fir forests of Mexico and at hundreds of forested sites along the California coastline. Reports from Mexico’s overwintering sites reveal that the area occupied by monarchs is at an all-time low. In California, monarchs cluster in many small sites scattered along the coast, making it more difficult to track the size of the population.

Now in its 17th year, the Western Monarch Thanksgiving Count is a remarkable citizen science effort to do just that. Over a three week period spanning the Thanksgiving holiday, dozens of volunteers visit scores of overwintering sites to count the number of monarchs. Overwintering monarchs along the California coastline have shown considerable declines since the count began. In 1997, the first year of the count, there were over 1.2 million monarchs at 101 sites. In 2013, just 211,275 were counted at 162 sites (see graph below).

Loss and degradation of both breeding and overwintering habitat, pesticide use, and drought—exacerbated by climate change—may all be contributing to this decline. Conservation scientists are concerned that the continuing drought in California and throughout the west may lead to even lower numbers in years to come.

Volunteer efforts such as the Western Monarch Thanksgiving Count are critically important to understanding the status of western monarch butterflies, and the 2013 overwintering season witnessed the most comprehensive site coverage to date, with 162 sites visited from Sonoma to San Diego Counties. Groups such as the Xerces Society, Monarch Alert, the Pacific Grove Museum of Natural History, and the Monarch Program are working to increase volunteer participation by providing outreach opportunities and engaging local citizens and students.




The data from the Western Monarch Thanksgiving Count is at

For information about the Western Monarch Thanksgiving Count and how to get involved, visit

Read more about Xerces’ Monarch Conservation Campaign, including efforts to conserve overwintering sites in California and restore breeding habitat in key regions of the United States at

Learn about efforts to conserve western monarchs by visiting the Monarch Joint Venture website:

Protecting the Life that Sustains Us

The Xerces Society is a nonprofit organization that protects wildlife through the conservation of invertebrates and their habitat. Since 1971, the Society has been at the forefront of invertebrate protection, harnessing the knowledge of scientists and the enthusiasm of citizens to implement conservation programs worldwide. To learn more about our work or to donate to the Society, please visit


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