
In this Sept. 11, 2020 file photo, a Monarch butterfly pauses in a field of goldenrod at the Flight 93 National Memorial in Shanksville, Pa.
An annual winter count by the Xerces Society recorded fewer than 2,000 butterflies, a massive decline from the tens of thousands tallied in recent years and the millions that clustered in trees from Northern California's Marin County to San Diego County in the south in the 1980s.
Western monarch butterflies head south from the Pacific Northwest to California each winter, returning to the same places and even the same trees, where they cluster to keep warm. The monarchs generally arrive in California at the beginning of November and spread across the U.S. once warmer weather arrives in March.
Comment: Mass mortality events caused by algae blooms are in the news more often recently, and the correlation of ocean anoxia with previous extinction level events is likely to be warning sign of what's to come: