Monarch butterflies wintering in California are recovering

The population of western monarch butterflies wintering along the California coast has recovered for the second straight year after a steep decline in 2020, but the population of orange-and-black insects is still well below previous levels, researchers said Tuesday.

Volunteers visiting sites in California and Arizona around Thanksgiving counted more than 330,000 butterflies, the highest number of these insects counted in the past six years. It’s been a promising recovery after the 2020 annual winter census recorded fewer than 2,000 butterflies. In 2021, the number recorded was 247,000.

“I think we can all celebrate and that’s really exciting,” said Emma Pelton, a conservation biologist at the Xerces Society, a nonprofit environmental organization focused on invertebrate conservation. “We were all so relieved last year when we had about 250,000 butterflies and to see that number increase even modestly this year is a really good sign that we got a second chance.”

Pelton said it’s not clear why the population has recovered, but one explanation could be that the eastern monarch butterflies, which winter in Mexico, could mix with their western counterparts.

“Some of that kind of leakage could happen, and I don’t think we understand the system fully enough to say what it is,” she said. “But I think one thing it’s not is that everything is fine or that we’ve all taken human actions that have magically made everything better.”

The population is still far below where it was in the 1980s when the number of monarchs was in the millions.

Scientists say butterflies in western states are at critically low levels due to destruction of their spurge habitat along their migratory route as habitation expands into their territory and use of pesticides and herbicides increases.

Along with agriculture, one of the main reasons for the monarch’s impending extinction is climate change, disrupting an annual migration of 4,828 kilometers (3,000 miles) synchronized with spring and the blooming of wildflowers.

Western monarch butterflies migrate south from the Pacific Northwest to California each winter, returning to the same locations and even the same trees, where they band together to keep warm. The monarchs breed several generations along the way thousands of miles before reaching California, where they generally arrive in early November. Once warmer weather arrives in March, they spread east of California.

On the east side of the Rocky Mountains, another monarch population from southern Canada and the northeastern United States travels thousands of miles to winter in central Mexico. Scientists estimate that the monarch population in the eastern US has declined by about 80% since the mid-1990s, but the decline in the western US has been even steeper.

Adult monarch butterflies live a few weeks, while monarch butterflies that winter congregate in trees and emerge in late summer and early fall can live up to nine months. As temperatures warm, they fly back to their breeding grounds, where their reproductive cycle begins again.

The census of western monarchs is conducted by trained volunteers over several weeks around Thanksgiving. Dating back to 1997, it has seen a loss of more than 95% of a population that previous studies have suggested was once in the tens of millions.

That year, the insects’ wintering habitat along California’s central coast was also hit by heavy rains, and volunteers reported more monarchs were being blown from their clusters and vulnerable to the cold, wet and predation, the Xerces Society said in a statement.

The group also usually conducts a second count after the new year. This year’s results, to be announced in February, shed light on how much winter storms have affected butterflies, said Isis Howard, a biologist for the protection of endangered species at the Xerces Society.

Howard said the New Year’s follow-up counts typically show a 30% to 50% drop in butterflies from the Thanksgiving count.

“Because the storms have been so intense and consecutive this year, it seems reasonable to assume that there could be increased mortality this winter, resulting in a smaller population that will kick off the breeding season next spring and summer.” ” She said.

© 2023 The Associated Press. All rights reserved. This material may not be published, broadcast, transcribed or redistributed without permission.