Daniel Roman, BAY NATURE
Since 1997, volunteers organized by the conservation group Xerces Society have counted western monarchs over Thanksgiving at the butterflies’ overwintering sites around coastal California, as part of the Western Monarch Thanksgiving Count. In 2020, the count hit an all-time low — less than 2,000 monarchs; a number, Bay Nature reported last year, that “represents an astonishing continuation of the near-total collapse of the western migratory population of the species over the last few decades.” Scientists then weren’t certain if any of the butterflies would come back at all. The preliminary reports out of this year’s count, however, suggest that they did, and in a big way.
“We’re well over 100,000 butterflies at this point,” said Emma Pelton, the Xerces Society’s senior endangered species conservation biologist and western monarch lead.
Data from over 200 monitoring sites show significantly greater numbers than last year. For example, more than 10,000 monarchs were counted at overwintering sites in Pacific Grove, Pismo Beach, and Big Sur. Last year, those three sites had less than 300 butterflies total. Similar trends are being reported from sites in Santa Cruz, Ventura, and Los Angeles. “We definitely haven’t seen an increase of this magnitude before,” Pelton said. The final numbers from the count overall are expected to be reported sometime in January.
Though this rebound gives cause for hope for the struggling monarch population, it does beg the question: How did it happen?
“That’s the question of the day,” Pelton said. “I would love to know.”
There’s a couple of different theories, with some studies to back them up. One hypothesis is that this year’s boom is due to an influx of monarchs from the eastern migratory population — which typically migrates between Mexico and the United States and Canada east of the Rocky Mountains — joining western monarchs, thereby adding to the population. Another theory, based on a recent study, suggests that monarchs are spending winters breeding in backyards in the East Bay instead of sheltering as they’ve traditionally done, probably due to warmer weather. Pelton, however, said she doesn’t find these theories very compelling — especially the latter one. “I’m not totally sure why we would think brief winter breeding in a different area of the coast would lead to that increase,” she said. “We see a lot of that sort of behavior in Southern California and we have for decades. It has not helped the population.”