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California's punishing winter storms pummel monarch butterfly population

It’s not just humans who have suffered from the recent winter storms. The extreme weather conditions have pummeled the endangered Monarch butterflies. But experts tell KPBS’ Alexander Nguyen there may be a silver lining at the end of the rainbow.

The population of the endangered monarch butterfly rebounded for a second year in a row, but this winter's punishing storms led to a nearly 60% die-off, according to data released earlier this month by the Xerces Society.

The Xerces Society's Thanksgiving count tallied 335,470 butterflies — a sharp increase from fewer than 2,000 in 2020. Last year's count was 247,000. This is still a drop compared to the millions in the 1980s and '90s.

"While it's really hopeful that we have higher numbers there, it's also pretty normal to have declines with crazy climatic events," said Pam Horsley, the entomology collections manager at the San Diego Natural History Museum.


Not all monarchs make it through the winter season, but the usual die-off range is 38% to 49%. This year's higher population count, however, gives Horsley hope.

"At least that means that there's probably going to be more survivors, as well," she said. "So that gives me hope that, even if it's been a cold, wet winter, that there will be more survivors here in the spring flying out soon."

Pat Flanagan, with the Butterfly Farm in North County, said monarch butterflies were adaptive, so, despite the punishing storms, he thinks that it looks promising for the species for the spring.

“It wasn't really what we wanted to have happened," he said. "But I feel like the monarchs are very resilient, and I would expect, especially with all this rain, that we'll see a lot of plant material this summer, not just for monarchs but for all butterflies."

Experts say that, with all the rain we've been having, now is a good time to start planting native plants — especially native milkweed. It's the only plant where female monarchs will lay their eggs.


Weather extremes attributed to climate change are generally not a great thing for vulnerable species such as the monarch butterflies. Horsley said there was a silver lining amid the wet weather we've been having.

"While it might affect the monarch's survival ability, at least if the host plants are doing really well with wetter weather that will give them a better opportunity perhaps to survive," Horsley said.

Though San Diego is not known as a huge overwintering site for monarch butterflies, we have monarchs year-round here, said Ann Baldridge, executive director at the Resource Conservation District of Greater San Diego County.

So it's important to create habitats for them.

"They need both breeding habitat and they need nectaring habitat where they can go and stock up on food for energy for flying," she said. "So planting milkweed is the No. 1 thing that we can do.”

The Resource Conservation District has packets of milkweed seeds that people can request for free to plant in their gardens.

Baldridge said scientists don't really know why the monarch butterfly population is rebounding, but it's good that more efforts are being made to preserve the species.

The low count in 2020 "was a huge call to action, and a lot of people have really gone out and supported monarchs, so many organizations, agencies and individuals are doing great work to create habitat and support them," she said.

There has been a big push in the Central Valley to create more monarch habitats because the key overwintering sites for the butterflies are along the Central Coast, Baldridge said.