California’s monarch butterfly population has declined by 99.9 percent between 1980 and 2020, with numbers returning to near record lows after a short-lived increase from 2021 to 2023, according to a May 2 announcement. The decline is raising concerns among scientists and conservationists who monitor the species’ migration along the California coast.
The issue matters because monarch butterflies are an important part of the ecosystem, serving as pollinators and indicators of environmental health. Their dramatic population drop signals broader challenges facing native wildlife in the state.
Scientists say habitat loss, pesticide use, and the disappearance of milkweed—the only plant where monarchs lay eggs—are major reasons for this decline. Climate change is also having an effect by changing weather patterns and disrupting migration timing.
Monarchs can still be seen at several locations in California despite lower numbers. Sites include Natural Bridges State Beach in Santa Cruz, Fiscalini Ranch Preserve in Cambria, Coronado Butterfly Preserve managed by Santa Barbara Land Trust, Goleta’s Ellwood Mesa Open Space, Bodega Dunes Campground in Bodega Bay, Point Mugu State Park in Ventura County, Pismo Beach, and Pacific Grove. These areas are monitored annually by volunteers and scientists who track overwintering populations.
The Western Monarch Thanksgiving Count provides annual data on population trends through surveys conducted from mid-November to early December and again around New Year’s Day. These efforts are coordinated by groups like the Xerces Society using trained volunteers who help gather information about overwintering sites.
People interested in helping can join local count teams or report sightings through projects such as the Western Monarch Milkweed Mapper website. Other actions include planting native milkweed or nectar plants free of pesticides at home and reducing chemical use overall.
Efforts like these may support monarch recovery over time if enough individuals participate.
