A population of Western monarch butterflies that overwinter on the California coast continues to exist
close to historical sites, according to the latest figures for the year. This adds to the growing concern that long-term population decline may become the norm.
About 12,260 monarch butterflies were recorded at 249 long-term winter habitats during surveys conducted from late November to early December 2025, according to the 29th annual Western Monarch Count report released Wednesday by the Xerces Society, a nonprofit environmental organization. The count relies on hundreds of trained volunteers and partner organizations to count the monarchs as they congregate in coastal trees.
The total is the third lowest since the count began in 1997, behind the 9,119 kings recorded in 2024 and the record low of 1,901 in 2020. According to a Xerces Society news release accompanying the new data, the population of the west remained in the low millions in 1980.
Although the number of monarchs naturally fluctuates from year to year due to climate and breeding success, research led by ecologists Cheryl Schultz and Elizabeth Crone found that the western monarch population has declined by about 10% per year since the 1980s, driven by a combination of habitat loss, pesticide use and climate change. On the contrary, this winter’s numbers, although slightly higher than last year’s, still fall well below what can be considered stable.
“This seems to be common in 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 is nothing unexpected about this year’s theme, but that alone is worrying.”
Low population levels also make monarchs more vulnerable to short-term depression and long-term stressors, says Isis Howard, a conservation expert with the Xerces Society.
Despite the low numbers, some coastal sites continued to have large collections. Natural Bridges State Beach in Santa Cruz County recorded its highest number this season, with about 2,500 kings seen in early December. Other relatively large populations have been found on private property near Big Sur in Monterey County and Lighthouse Field State Beach in Santa Cruz.
In Santa Cruz, researchers and conservationists also sent ultralight radio tags to better understand how butterflies move between overwintering trees, information that could help improve how overwintering habitat is managed.
Loss of long-term winter 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 legal enforcement began, mainly due to coastal development and what the non-profit organization called “improper” tree removal.
Last year alone, at least three active monarch overwintering sites were severely damaged by improper logging, according to the Xerces Society. Continued development proposals threaten monarch groves in parts of Hayward and Ventura County, the nonprofit said, although other communities such as Albany’s UC Gill Tract Community Farm have shown it is possible to continue development while protecting the monarch’s overwintering habitat.
“Western monarchs are in serious trouble,” Emma Pelton, senior biologist for the Xerces Society, said in a statement. “Our window for action is shrinking, and our conservation efforts must be accelerated.”
