The annual Western Monarch Count was lower by about 100,000 butterflies in 2023 than the previous count.
Across 256 sites, volunteers counted 233,394 monarch butterflies from Nov. 11 through Dec. 3, 2023, according to KNX News’ Margaret Carrero. In 2022, more than 330,000 butterflies were counted.
The majority of overwintering monarchs resided in San Luis Obispo and Santa Barbara counties.
Isis Howard, with the Xerces Society, said they have a few ideas as to why the count was lower this time.
“Although it's pretty difficult to pinpoint one or two exact reasons, many factors contribute to population fluctuations,” she said. “This year, we may have seen smaller numbers at overwintering sites due to last year's storms.”
Emma Pelton, a monarch biologist at Xerces Society, said the reason for the lower count is multifaceted, pointing to habitat loss, pesticide contamination, and climate change.
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“This includes both the loss of the overwintering forests that they rely on along the Pacific coast, but more broadly across North America, we know we've seen widespread loss of the host plant milkweed that their caterpillars rely on to grow up,” she said.
Migratory western monarchs remain at 5% of the numbers seen nearly 40 years ago. At that time, there were millions of monarch butterflies overwintering along the California coast, according to the Xerces Society.
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