SANTA CRUZ — The number of western monarch butterflies has rebounded from dismal low numbers recorded in 2020 — at least temporarily — according to the Xerces Society for Invertebrate Conservation, which released its Thanksgiving Count 2021 data on Tuesday.
Community scientists have documented more than 247,000 monarch butterflies across the West. That’s more than 100 times more than the previous year’s total of less than 2,000 monarchs, said Emma Pelton, head of the Xerces Society Western Monarch, and the highest number on record since 2016.
In Santa Cruz County, only 711 monarchs were recorded during the 2020 Thanksgiving count. Last year, more than 5,400 butterflies were documented clinging to eucalyptus trees and fluttering through wintering sites.
“We are delighted with the results and hope this trend continues,” Pelton said during a webinar on Tuesday. “There are so many environmental factors at play across their range that there is no single cause or definitive answer to this year’s rise, but hopefully that means we still have time protect migration.”
Monarch butterfly populations in Santa Cruz and across the state have dropped dramatically in recent years. This trend is linked to habitat degradation and pesticide application, as well as the impact of climate change. The butterflies overwinter from about October through March on the California coast from Mendocino County south to San Diego.
The Xerces Society has sponsored the Thanksgiving Count since 1997, which is done by volunteers. Since then, the population of iconic species has fallen by 95%, according to data from the Xerces Society, which shows the numbers are in the millions.
“So this year is not a recovery, and it will take several more years to figure out if this is the start of a trend or just a blip,” Pelton said.
The 2021 count was marked by record participation: community scientists observed 283 overwintering sites. Butterfly numbers were trending south, reported Xereces Society conservation biologist Isis Howard.
Monarch counts were more concentrated on the central coast, but even more so in southern California.
Volunteers from the San Francisco Bay Area and Central Coast typically see the bulk of monarch numbers during the annual count. But this year, from Mendocino to San Mateo County, few butterflies have been documented. Santa Cruz County marked the first sighting of butterfly clusters of more than 1,000 individuals, Howard said. Pacific Grove has seen 14,000 monarchs wintering at the sites, and further south volunteers from San Luis Obispo County have documented over 90,000 monarchs.
Scientists still know why the butterflies flocked to the southern regions.
Weather could be in play. According to Pelton, dry spring and summer conditions can cause first-generation monarch butterflies to emerge from their cocoons. These first-generation butterflies that breed in California and at sites in Santa Cruz, such as Lighthouse Field and Natural Bridges, are critical to maintaining the species’ population.
It’s also unclear what factors – weather or otherwise – led to the population surge in 2021. Pelton warned that a good year does not predict future conditions for the beloved butterfly, which is expected to be listed under the Endangered Species Act in 2024.
“These numbers are going to continue to fluctuate until we really get to the underlying reasons why we’ve seen these huge declines over the decades,” Pelton said.