Monarch butterfly numbers plummet 86 percent in California

CAMARILLO, Calif. — The number of monarch butterflies turning up at California’s overwintering sites has dropped by about 86 percent compared to only a year ago, according to the Xerces Society, which organizes a yearly count of the iconic creatures.

That’s bad news for a species whose numbers have already declined an estimated 97 percent since the 1980s.

Each year, monarchs in the western United States migrate from inland areas to California’s coastline to spend the winter, usually between September and February. 

“It’s been the worst year we’ve ever seen,” said Emma Pelton, a conservation biologist with the Xerces Society who helps lead the annual Thanksgiving count. “We already know we’re dealing with a really small population, and now we have a really bad year and all of a sudden, we’re kind of in crisis mode where we have very, very few butterflies left.”

Results from the count so far show that the number of monarchs at 97 California overwintering sites has dropped from around 148,000 in 2017 to just over 20,400 this year. Counts for dozens of other sites are still being tabulated, but the outlook is troubling, Pelton said.

What’s causing the dramatic drop-off is somewhat of a mystery. Experts believe the decline is spurred by a confluence of unfortunate factors, including late rainy-season storms across California last March, the effects of the state’s yearslong drought and the seemingly relentless onslaught of wildfires that have burned acres upon acres of habitat and at times choked the air with toxic smoke.

The Thomas Fire last year burned almost 300,000 acres, including areas important for monarch breeding and migration, Pelton said. More recently, the Woolsey Fire damaged at least four monarch butterfly overwintering sites in the Malibu area, according to Lara Drizd, a wildlife biologist with the U.S. Fish and Wildlife Service in Ventura.

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