Monarchs decreased across California last year but rose by about a third in West Marin, according to the Xerces Society for Invertebrate Conservation. During its annual Thanksgiving count, around 60 monarchs were spotted in Stinson Beach and roughly 3,000 were counted in Bolinas, many at a grove of eucalyptus trees that has been targeted for removal. Monarchs arrived at the site early, then bounced back and forth to two other sites in town and stayed through the new year, dwindling slightly as heavy rain set in. Another Bolinas site that saw over 1 million monarchs in 1997 was eliminated this winter after the property owner removed trees that threatened to fall on the property. Northern California provides important over-wintering habitats for the butterflies, which mostly spend time in Southern California; 76 percent of monarchs counted were in San Luis Obispo and Santa Barbara Counties alone. David Ainley, an ecologist and Bolinas resident who has done his own research on monarch patterns, rejects the notion that monarchs are using local sites to overwinter, saying they are temporarily stopping before heading south to the more favorable conditions. Mia Monroe, a National Park Service ranger and a co-founder of the West Coast count, disagrees. “I don’t see any evidence that they’re just passing through,” she said. “Overwintering means that the clusters persist into the new year and there were pretty consistently good numbers.”
This story was corrected on March 13 to reflect updated numbers.