upper waypoint

Monarch Butterflies Are on the Decline in California. Here’s Why

Save ArticleSave Article
Failed to save article

Please try again

A monarch butterfly lands on a plant growing in the schoolyard at International Community School in Oakland on Oct. 20, 2022. (Beth LaBerge/KQED)

California’s iconic monarch butterfly population saw a sharp decline this year, which biologists attribute to the hot summer and fall temperatures across the state affecting the species’ migratory path.

The latest Western Monarch Count by Xerces Society recorded 9,119 overwintering monarch butterflies — those that travel to warmer climates in the winter — in California, marking the second-lowest population since tracking began in 1997. This sharp decline follows three consecutive years of over 200,000 monarchs and remains well below the millions observed in the 1980s.

“The specific drop we saw this year largely attributed to the really hot temperatures and the drought that we saw across the West in July, somewhat into August and again in September and October, when that migratory generation should be making its way to the overwintering sites,” said Emma Pelton, an endangered species biologist with the Xerces Society for Invertebrate Conservation.

Santa Cruz County had the most overwintering monarch clusters this year, with Lighthouse Field State Park reporting 1,406 butterflies, Natural Bridges State Park counting 1,400, and Moran Lake recording 645. The fourth-largest site was Pismo Beach Monarch Butterfly Grove in San Luis Obispo County, with 556 monarchs recorded in late November. Skywest Golf Course in Hayward ranked fifth with 477 butterflies.

Other locations with higher densities of monarchs include the Pacific Grove Butterfly Sanctuary in Monterey County, which had 228, and UC Gill Tract Community Farm in Alameda, which recorded 196 and was one of the few sites to see a population increase this year.

Sponsored

Meanwhile, some historically significant sites experienced drastic declines. The Goleta Monarch Butterfly Grove at Ellwood Mesa had almost no clusters, with only three monarchs spotted across multiple locations. A privately-owned Santa Barbara site managed by The Nature Conservancy, which hosted 33,200 monarchs last winter, dramatically dropped to 198 this season.

Experts say the decline is caused by habitat loss, pesticide exposure, and climate change. Record-high temperatures and drought throughout the summer and fall months last year likely also contributed to the drop. In January, fires in Los Angeles County burned tree groves where monarchs overwinter, including a site in Lower Topanga Canyon.

The western monarch population, which migrates separately from eastern monarchs overwintering in Mexico, relies on California’s coastal tree groves for shelter. Experts say voluntary efforts like pollinator gardens have helped prevent even steeper declines but that broader policy changes are needed.

Related Coverage

“There’s a huge number of people that care about monarchs and are planting habitat or trying to protect the species. But the evidence points to how we need this work done at a much higher level,” Pelton said, referring to the U.S. Fish and Wildlife Service’s proposal to list monarchs as a threatened species under the Endangered Species Act.

If approved, the proposal would provide improved protection for monarch overwintering habitat in California and more incentives for habitat restoration. A public comment period on the listing is open until March 12, and Xerces Society is asking individuals to sign on to support the listing.

lower waypoint
next waypoint