California’s monarch butterfly population remains at historically low levels, according to a May 2 announcement. After a short-lived increase between 2021 and 2023, the number of western monarch butterflies has returned to near record lows.
The decline in monarch populations is significant because these butterflies play an important role in pollination and are considered an indicator species for ecosystem health. Their migration from Canada to California’s coast is studied by schoolchildren and scientists alike, highlighting their ecological importance.
Scientists say that habitat loss, pesticide use, and the disappearance of milkweed—the only plant on which monarchs lay eggs—are major reasons for the sharp decline over the past four decades. Climate change is also believed to be disrupting weather patterns and migration timing. Monarchs cluster during winter in Central and Southern California groves such as eucalyptus or Monterey pine trees, where thousands once gathered on a single tree at peak times. Sites like Natural Bridges State Beach in Santa Cruz, Fiscalini Ranch Preserve in Cambria, Coronado Butterfly Preserve in Santa Barbara County, Ellwood Mesa Open Space in Goleta, Bodega Dunes Campground in Bodega Bay, and Point Mugu State Park continue to serve as important refuges despite lower numbers today.
The Western Monarch Thanksgiving Count provides annual data on population trends through community science efforts coordinated by organizations like the Xerces Society. Volunteers survey overwintering sites each year from mid-November through early January. These counts are vital for understanding changes over time.
People interested in helping can join local count teams or report sightings through projects such as the Western Monarch Milkweed Mapper website. Planting native milkweed and nectar plants without pesticides also supports monarch recovery efforts.
