Last week we visited our local monarch butterfly sanctuary, in Pacific Grove, and enjoyed reading the informational signage and watching the insects fluttering in the sunshine. It turns out Monterey County has some twenty overwintering sites, from Moss Landing to Big Sur, while the entire state has 400+. The core of the Western monarch overwintering range is in Santa Barbara and San Luis Obispo Counties. (Eastern monarchs—that is, east of the Rocky Mountains—migrate to the oyamel fir forests north of Mexico City to overwinter.)
The Xerces Society for Invertebrate Conservation, based in Portland, Oregon, has just launched its annual Thanksgiving Monarch Butterfly Count (Nov. 12–Dec. 4), with a second count coming up around New Year's Day. (The overwintering season runs approximately October through February.) In 2020, the official count in the PG sanctuary was zero, and only about 2,000 butterflies were found in the entire state—down from a high of over 1.2 million in 1997, the year the count was launched. Since 1997, the count has fluctuated at significantly lower levels, and the last several years have been dismal. Everyone thought the Western monarchs were about to go extinct.
But then last year, hopes were buoyed when the count was 13,608 in the PG sanctuary, and over 247,000 for the state as a whole. This year, the numbers seem to be similar: every Friday morning, volunteers from the Pacific Grove Museum of Natural History do a census, and last week the number stood at 12,328.
How are they counted? One by one, when they cluster in loose groups, and by estimating in larger clusters. Allison Watson, former director of education and outreach for the museum, said, "I begin at the tip of the branch, and count ten monarchs grouped together in the cluster. Based on the amount of space those ten monarchs occupy on the branch, I then count by groups of ten up the branch, until I count all of the monarchs on the branch."
In Mexico, meanwhile, the butterflies cluster so densely that individuals aren't counted; rather, the area of forest that they occupy is what matters, with 6 hectares (about 14 acres) being the minimum for sustained population health.
I could go on, but there's too much! If you're interested in reading more about these fabulous little insects, check out the Wikipedia page, which has a ton of information—including all 24 Asclepias (milkweed) species that the larvae depend on for food, as well as threats to their survival and conservation efforts. And more!
Here are a few photos (not mine).
I will end with a poem, "The Butterflies the Mountain and the Lake," a fragment from a larger poem by Shane McCrae:
It's Saturday most often neighbor we
Are walking with our daughter lately even when / We talk together
everywhere we go we want to go home everywhere / But oh
hey did you see that story
about the butterflies the mountain and the lake
the / Butterflies monarch butterflies huge swarms they
Migrate and as they migrate south as they
Cross Lake Superior instead of flying
South straight across they fly
South over the water then fly east
still over the water then fly south again / And now
biologists believe they turn to avoid a mountain
That disappeared millennia ago / No
butterfly lives long enough to fly the whole migration
From the beginning to the end
they / Lay eggs along the way
Just as you and I most often neighbor
Migrate together in our daughter over a dark lake
We make with joy the child we make
And mountains are reborn in her
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