BACKSTORY
Every fall, monarch butterflies migrate south; Eastern monarch populations head to Mexico, while Western monarchs visit California’s coastal groves. But much of the overwintering habitat on both sides of the border has disappeared, and scientists say that development, along with the loss of the native milkweeds the butterflies rely on, has led to plummeting monarch numbers. In 1997, California’s groves held more than a million butterflies; in 2013, there were fewer than 150,000 (“A native butterfly finds merit in a non-native tree,” HCN, 12/23/13).
FOLLOWUP
In January, experts announced that Western monarch butterfly populations have hit a new low. Just 28,000 were found in California groves this fall, a 99 percent decline from the 1980s. Scientists blame pesticide use, climate change and habitat destruction from construction, agriculture and wildfires, especially in the state’s Central Valley, coastal foothills and Sierra foothills. Although Eastern monarch populations rebounded a bit this year, over the last four decades their numbers have dropped about 80 percent.
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This article appeared in the print edition of the magazine with the headline The West’s monarch migration is disappearing.
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