The number of western monarch butterflies overwintering along the California coast continues to remain
near historic lows, according to a new annual count. This adds to growing concern that the population’s long decline may be becoming the norm.
Roughly 12,260 monarch butterflies were recorded across 249 overwintering sites during surveys conducted from late November through early December 2025, according to the 29th annual Western Monarch Count released Wednesday by the Xerces Society, a nonprofit environmental organization. The count relies on hundreds of trained volunteers and partner organizations to tally monarchs as they cluster in coastal tree groves.
The total is the third-lowest tally since the count began in 1997, after the 9,119 monarchs recorded in 2024 and the record low of 1,901 in 2020. According to a Xerces Society news release accompanying the new data, western monarch populations regularly numbered in the low millions in the 1980s.
Although monarch populations naturally fluctuate from year to year due to weather and breeding success, research led by ecologists Cheryl Schultz and Elizabeth Crone has found that western monarch populations have declined by about 10% per year since the 1980s, driven by a combination of habitat loss, pesticide use and climate change. Against that backdrop, this winter’s numbers, while slightly higher than last year’s, still fall well below what would be considered stable.
“This does appear to be the new normal for western monarchs, and it’s very concerning,” said Dan Fagin, a professor of science journalism at New York University who is writing a book on monarch butterflies. “There’s nothing unexpected about this year’s total, but that in itself is troubling.”
Low population levels also make monarchs more vulnerable to short-term stress and long-term pressures, said Isis Howard, a conservation biologist with the Xerces Society.
Despite the low overall numbers, some coastal sites continued to host relatively large clusters. Natural Bridges State Beach in Santa Cruz County recorded the highest count this season, with about 2,500 monarchs observed in early December. Other relatively large populations were found at a private property near Big Sur in Monterey County and Lighthouse Field State Beach in Santa Cruz.
In Santa Cruz, researchers and conservationists also deployed ultralight radio tags to better understand how butterflies move between overwintering groves, information that could help improve how overwintering habitat is managed.
Loss of overwintering habitat remains a major threat, conservationists say. According to Sarina Jepsen, director of the Xerces Society’s endangered species program, more than 60 overwintering sites have been destroyed since formal tracking began, largely due to coastal development and what the nonprofit called “inappropriate” tree removal.
In the last year alone, at least three active monarch overwintering sites were significantly damaged by inappropriate tree cutting, according to the Xerces Society. Ongoing development proposals threaten monarch groves in parts of Hayward and Ventura County, the nonprofit said, though some communities such as Albany’s UC Gill Tract Community Farm have shown it is possible to continue development while protecting monarch overwintering habitat.
“Western monarchs are in serious trouble,” said Emma Pelton, a senior conservation biologist with the Xerces Society, in a statement. “Our window for action is narrowing, and our conservation efforts must accelerate.”
