California monarch butterfly population down 86 percent in one year

Tiffany Camhi, THE CALIFORNIA REPORT, KQED

“We think that it has to do with habitat loss, the increasing high use of pesticides and the loss of the milkweed populations, which is the plant the monarch needs to lay its eggs on,” Monroe said.

California’s coast, from Bolinas to Pismo Beach, is a popular overwintering site for the western population of monarch butterflies. Historically, you could find millions of the orange and black winged invertebrates around this time of year, using coastal eucalyptus trees as shelter.

But there’s been a troubling trend over the past few decades. Each year, fewer monarchs have been showing up to overwinter on the state’s coast, according to preliminary numbers from the Xerces Society, an environmental conservation nonprofit. The group’s annual Thanksgiving count found the 2018 population of these butterflies is down to 20,456 compared to 2017’s 148,000. That’s a one year, 86 percent decline.

“It’s been hard for me, as I remember the millions of monarchs of the 1980s,” said Mia Monroe, a Bay Area-based Xerces Society member who helps lead California’s monarch population count. “We only have less than one percent of the monarchs that we once historically had.”