Monarch Butterfly Population Drops by 30 Percent in California

The 2023 population is only 5 percent of its size in the 1980s, according to a study.

A Monarch butterfly is pictured at a butterfly farm in the Chapultepec Zoo in Mexico City on April 7, 2017. Pedro Pardo/AFP via Getty Images

The population of western monarch butterflies in California has dropped by 30 percent since 2022, according to the most recent count conducted by the Xerces Society.

The count, done at 256 sites across the western United States from Nov. 11 through Dec. 3, 2023, shows about 233,400 western monarch butterflies stayed at sites along the California coast during the winter—about 102,000 fewer than the year before.