Numbers of monarch butterflies wintering on coast fall to new lows
The iconic monarch butterflies have some dedicated friends in Sonoma County. And it looks like they’ll need them.
Two million years or so ago, scientists say, the regally colored orange, black and white insect we call the monarch was a tropical butterfly. Gradually, it spread across North America, following abundant fields of its essential food, milkweed. But the northern climes also held deadly cold winters, so the fragile monarch adapted an unusual survival strategy: after feeding and breeding in northern fields all spring and summer, it beat wings south in vast numbers to safely wait out the winter in protected, warmer locales.
The butterfly now migrates distances of hundreds and even thousands of miles each year.
Historically, one western population of monarchs has unerringly headed to California from as far away as Idaho and Washington state to concentrate in select, sheltered spots along the coastline. A few dozen special groves from Mendocino to Baja have annually hosted up to many millions of traveling monarchs. Safe from freezing temperatures and fierce winter storms, the butterflies rouse again in early spring to begin their northward trek once more.
But not this year. According to the annual Thanksgiving monarch butterfly count, after years of steady decline, only 2,000 returned to California in 2020, a population decline of 99.99% from counts taken as recently as the 1980s.
Of the 12 historically active monarch overwintering sites in Sonoma County, none were occupied when volunteers checked them this winter.
“Everyone’s pretty heartbroken about the count,” Noelle Johnson said last week. Johnson is a conservation planner with Gold Ridge Resource Conservation District and program manager for its Sonoma Coast Monarch Overwintering Site Protection and Enhancement Project. She is one of a dedicated corps of local scientists, conservationists and volunteers working with the newly funded project to try and head off the butterfly’s extinction.
Few good groves
Finding and protecting monarch overwintering sites is one of the goals of the Gold Ridge district’s monarch project.
Most of the known overwintering sites in Sonoma County are on public land — in state parks, county regional parks or Wildlife Conservation Board-owned preserves. One site, a grove of eucalyptus trees at the northern edge of the Bodega Dunes Campground overlooking Bodega Bay, has been a reliable destination for butterfly watchers to find clusters of monarchs, until this year.
Despite the missing butterflies, there may be a silver lining, according to Mia Monroe, a Bay Area volunteer with Xerces Society, an international nonprofit focused on the conservation of invertebrates and their habitats.
“We may not know all the monarch winter sites; some may remain on private land,” she said.
In 2000, as a volunteer with Xerces, Monroe took over coordination of the annual Thanksgiving monarch count, and she continues in that role today.
“I go to sites, locate monarchs, count them, do field reconnaissance, lead volunteer training to conduct the counts,” she explained.
Xerces, along with several other organizations, first proposed in 2014 to the U.S. Fish and Wildlife Service that monarchs be added to the list of threatened and endangered species. In December, after studying monarch populations for several years, the department decided not to include monarchs on the list, saying there were higher priorities for listing. However, the department said the monarch could be added to the list in the future.
Monarchs under pressure
Why the monarchs have stopped returning is still an open question for scientists. But all agree on one thing: the hardy fliers are facing an unprecedented number of challenges, all at the same time.
According to Stu Weiss, chief scientist with Creekside Science, a Northern California consulting firm specializing in conservation, habitat restoration and endangered species studies, the complexity of monarch migration leaves them vulnerable.
“A combination of factors are pushing things over the edge,” he said. “Not just climate extremes, but toxic pesticides, loss of habitat, smoke from wildfires and especially the loss of native milkweed.” The milkweed plant is the monarch caterpillar’s only food.
And in recent decades, as tree groves have been logged or removed for construction and agriculture, fewer protected sites remain for overwintering monarchs.
Monarchs are very particular about the sites they choose to overwinter in, Weiss said. Their lives depend on it.
“The tree groves have to provide several essential elements. They have to be near a source of drinking water and very close to the sea, so they don’t freeze,” Weiss said. “The butterflies need wind shelter, so dense groves in sheltered ravines are usually preferred. And they need a well-lit spot — some direct sun and dappled light. What they really like to find is a medium-to-large gap in the middle of a grove.”