Monarch butterfly populations rebound in California

(CN) — The population of Western monarch butterflies appears to have bounced back in California, reversing a trend that many feared pointed to a swift decline toward extinction. 

In 2020, a Thanksgiving count administered by the Xerxes Society for Invertebrate Conservation found less than 2,000 Western monarchs at the overwintering sites along the Central Coast of California, prompting fears the species’ doom may be imminent. 

But this year an unofficial count has shown that at least 50,000 individual butterflies can be accounted for at various sites along the coast including Santa Cruz, Pismo Beach and Ventura.

"This is certainly not a recovery but we're really optimistic and just really glad that there are monarchs here and that gives us a bit of time to work toward recovery of the Western monarch migration," Sarina Jepsen, director of Endangered Species at Xerces Society for Invertebrate Conservation, told The Associated Press on Wednesday. 

At one site in Big Sur, there were at least 10,000 butterflies present when counters arrived, meaning more butterflies appeared at the one privately maintained site this year than appeared along the entire Central Coast, which spans from south of San Francisco to north of Los Angeles, in 2020. 

The same number of butterflies were counted at sites in Pismo Beach and Pacific Grove, which is known as “Butterfly Town USA” and is famed for its celebration of the colorful insects. 

Every year, thousands of butterflies flee the cold winter temperatures of the Pacific Northwest for the more temperate climes of California, where they spend the winter huddled in clusters to keep warm. There are more than 100 such cluster sites up and down the California coast. 

A particularly famous one is at the Natural Bridges State Park in Santa Cruz, which overlooks a windswept portion of the California coast, dotted by overhanging Eucaplytus trees and cypress. 

The butterflies begin to arrive in mid-October and their numbers peak in mid-November, which is why the Xerxes Society holds its annual count around Thanksgiving. 

The past few years have been depressing for those who appreciate the regal beauty of the Western monarch butterfly. Not only was the count alarmingly low last year, but it was well below the 30,000 threshold — the figure at which scientists believe the migration may collapse. 

While the most recent count furnished good news, the preliminary figure of 50,000 remains well below historical numbers recorded as recently as the 1980s, when millions of monarchs overwintered in California. 

Scientists are also cautious because of natural fluctuations in the butterfly population in California, a phenomenon they refer to as bounciness. 

"If we were to count 50,000 butterflies this year, that would be about 25% of the count five years ago,” Emma Pelton, a senior conservationist at Xerxes, recently wrote. “In other words, if this count came in a few years ago, we would be quite concerned with how low these early numbers are.”

Scientists attribute the uptick in the population to good luck with weather, habitat and competition from other species. A warm, dry summer with cooler autumn temperatures, which has been the case for California in 2021, likely benefit the monarch population. 

But while scientists are eager to celebrate the positive news, they warn that one year doesn’t tell much in the way of long-term trends. 

“With only one year of a population increase, it is impossible to say whether this is the population clawing its way back from the brink or a blip in the continuation of the migration’s decline,” Pelton wrote. “We won’t know this until we have more years with either more or fewer monarchs.”

Residents interested in helping to bolster the monarch population in California are encouraged to plant milkweed in their yards. The use of herbicides to rid agricultural land of milkweed is one of the largest reasons for the species’ decline, according to scientists, and people should restrict their use of pesticides that could be harmful to the butterflies themselves.

“Though we are likely to see increases in the size of the migratory western monarch population this year, and that is reason for hope, the population is still dangerously close to collapse and there remains an urgent need to address the threats that this butterfly faces,” Pelton said. 

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