Population of Western monarch butterflies in California decreased by 30% last year. Is climate change the cause of the extinction of insects?


Butterflies have been making a comeback, but their populations are still significantly lower than they were in the 1980s, when millions of monarchs could be found. Last year, the number of western monarch butterflies that overwintered in California decreased by 30%, which researchers attribute to the excessive rainfall. The Xerces Society, an environmental nonprofit organization focused on insect conservation, reported that volunteers who visited sites in California and Arizona during Thanksgiving counted just over 230,000 butterflies, compared to 330,000 in 2022. Despite the fact that the butterfly population has recovered to hundreds of thousands in recent years, it remains far lower than it was in the 1980s when millions of monarchs were observed. The destruction of milkweed habitats along their migratory route due to housing construction and the increased use of pesticides and herbicides are among the main reasons why scientists say that butterfly populations are critically low in western states. Climate change is also one of the main drivers of the monarch’s threatened extinction, disrupting the butterfly’s annual 3,000-mile (4,828-kilometer) migration, which is synchronized with the blooming of wildflowers in the spring.

“Climate change is making things harder for a lot of wildlife species, and monarchs are no exception,” said Emma Pelton, a monarch conservation biologist with the Xerces Society. “We know that the severe storms seen in California last winter, the atmospheric rivers back to back, are linked at some level to our changing climate.”

Monarchs from the Pacific Northwest migrate south to California during winter, returning to specific locations and even the same trees where they gather for warmth. Before reaching California in early November, they reproduce multiple times along their journey. When the weather becomes warmer in March, they disperse eastward from California.
On the eastern side of the Rocky Mountains, a separate monarch population travels to central Mexico from southern Canada and the northeastern United States. While scientists estimate that the eastern U.S. monarch population has declined by about 80% since the mid-1990s, the decrease has been even more severe in the western U.S.

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