Western Monarch Butterfly Population Declines to Near Record Low

San Francisco, Calif. Jan. 30, 2025— Following efforts by hundreds of volunteers and partners to count overwintering monarch butterflies in California, the 28th annual Western Monarch Count has reported a peak population of just 9,119 butterflies this winter. This is the second lowest overwintering population ever recorded since tracking began in 1997 and coincides with monarch butterflies being proposed for protection under the U.S. Endangered Species Act.

This number is a sharp decline from the past three years, when more than 200,000 overwintering western monarchs were observed each year. It is only slightly above the all-time low of less than 2,000 monarchs in 2020, and well below the millions of butterflies observed in the 1980s that scientists consider a stable population level.

“The population’s size is extremely concerning,” said Emma Pelton, an endangered species biologist with the Xerces Society for Invertebrate Conservation. “We know small populations are especially vulnerable to environmental fluctuations, and we think that’s what happened this year. The record high late summer temperatures and drought in the West likely contributed to the significant drop-off we saw in the third and fourth breeding generations.”

Pelton says monarchs encounter a variety of threats across their migratory range, including pesticides, habitat loss, and increasingly severe weather exacerbated by climate change. January’s fires in Los Angeles County burned tree groves where monarchs overwinter, including a site in Lower Topanga Canyon.