Low counts of overwintering monarchs trouble experts who see a potential species collapse.

Every late fall along the California coast, hundreds of trained volunteers crane their necks to look up into trees and count a precious pollinator, western monarch butterflies. This year’s 29th annual count, led by the Xerces Society for Invertebrate Conservation, yielded the third-lowest tally since counting began in 1997, with 12,260 monarchs across 249 sites during the peak overwintering period, between late November and early December.

In “Butterfly Town,” Pacific Grove, the official number was 188 inside the city’s Monarch Butterfly Sanctuary, down from 228 in 2024 and 6,508 in 2023. One week later, on Dec. 12, the sanctuary peaked at 226, reports Natalie Johnston, education manager at the Pacific Grove Museum of Natural History.

Johnston says the hope was for a rebound this year, similar to 2021 when numbers in P.G. jumped to over 13,000, a year after the count was zero. Monarch populations can be “bouncy,” she says, but this year the bounce for P.G. didn’t happen. A Xerces biologist signaled an alarm on Jan. 29. “Western monarchs are in serious trouble. The migration is collapsing,” Emma Pelton, senior conservation biologist with Xerces, said in a statement.

Scientists believe pesticides and destruction of overwintering habitats are contributing to low numbers. More than 60 overwintering sites have been destroyed since 1997, according to Xerces – three in the last year were damaged through tree removal.

Two years ago, the U.S. Fish and Wildlife Service was preparing to list western monarchs as a threatened species which would have brought protection. That decision is now on hold under the Trump Administration.