The orange-winged insect’s population increased from 2,000 in 2020 to nearly 250,000 in 2021
Monarch butterfly populations have increased a hundredfold in overwintering sites in California after historically low numbers in 2020, per the Xerces Society for Invertebrate Conservation. Volunteers observed less than 2,000 monarchs in the state at the society’s annual Thanksgiving count in 2020. Last year, they counted more than 247,000.
Though monarch numbers increased, they are far from the millions that California saw in the 1980s. In 2020, this represented a 99.9 percent decline, write Pelton and Stephanie McKnight on Xerces’ blog. Scientists think threats including habitat loss and pesticide use caused population numbers to plummet.
The United States is home to two populations of monarch butterflies that are separated by the Rockies. The eastern population flies south to Mexico for the winter, while the western one overwinters in California.
“I don’t recall having such a bad year before and I thought they were done,” Moe Ammar, president of Pacific Grove Chamber of Commerce, told the Associated Press’s Haven Daley and Olga R. Rodriguez last November. “They were gone. They’re not going to ever come back and sure enough, this year, boom, they landed.”
Scientists don’t know exactly why the monarch count increased last year, but some hypotheses include ideal weather conditions, fewer pesticides used during the Covid-19 pandemic, wildfires preparing the ground for wildflower growth, new additions from the eastern population and less competition, reports Alissa Greenberg for NOVA Next. It’s most likely a combination, experts tell NOVA.
“It's crucial to remember that the modest uptick we're seeing is not population recovery or even evidence of an upward trajectory,” researchers write in a Xerces’ blog. “The population is still dangerously close to collapse, and there remains an urgent need to address the threats that this butterfly faces.”
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