In California, the Number of Monarch Butterflies Has Dropped by 30 Percent

Every fall, monarch butterflies from west of the Rocky Mountains start arriving in California to wait out the winter.

The orange and black insects are closely monitored, because the number of western monarchs that come to California each year has dropped precipitously since the 1980s, when it was common to see millions annually.

This past winter, scientists and volunteers went to more than 250 overwintering sites in the state and counted around 233,000 butterflies, a 30 percent drop from the previous winter, according to a report released this week by the Xerces Society for Invertebrate Conservation.

The decline was probably caused by the severe storms that hit California in the winter of 2022, which may have been too intense for the insects to survive, according to Isis Howard, who coordinates the count for the Xerces Society. That caused the breeding season last year to begin with fewer butterflies, reducing the population that would return in the fall.

Monarchs were classified as endangered in 2022. A particularly steep downturn began in the winter of 2018, when about 30,000 monarch butterflies wintered in California, according to Emma Pelton, a monarch conservation biologist with the Xerces Society. Two years later, only 2,000 were counted across the state, and some of the groves that usually attract the most monarchs were devoid of them.

“In 2020, the bottom fell out,” Pelton told me. The moment prompted many “existential conversations in the monarch world” about whether the species would ever recover, she said. But in a “somewhat miraculous” turnaround, she added, the monarch population bounced back to around 200,000 in 2021, a figure similar to this week’s count.

There’s a lot we don’t understand about monarchs, so it’s difficult to say with certainty why their numbers have fluctuated so drastically. But environmental factors like changes in temperature and precipitation probably play a role. Experts generally believe that pesticide use, drought, climate change and habitat loss, from deforestation and other causes, have all contributed to a long-term decline of the species.

If you want to help monarchs thrive, you can plant native flowering plants in your garden, including milkweed, the only plant that monarch caterpillars eat. Make sure that the plants you buy from nurseries are pesticide-free, and limit your own pesticide use if you can.

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And before you go, some good news

An officer in the Sunnyvale Department of Public Safety has earned a reputation for solving some of the region’s toughest and longest-running cold cases.

The detective, Matt Hutchison, 38, has solved eight cases in the seven years since he joined Sunnyvale’s robbery and homicide team. Hutchinson’s unorthodox methods, especially in the face of sparse evidence, have helped him crack some of the department’s biggest cases, including the killing of Karen Stitt, a Palo Alto High School student who was murdered in 1982, which baffled more than 20 department detectives over the years.

Even more remarkable: Hutchinson has solved all those cases in his spare time, when not occupied with his regular duties.

Scott Ostler, a reporter at The San Francisco Chronicle, took a look at Hutchinson’s impressive record in a recent profile. “It’s this magic stuff that he does,” Rob Baker, the deputy district attorney for Santa Clara County, told Ostler. “He has solved more cold cases in three years than any single detective in the last 15.”