Washington DC [US], March 11 : A study has been released, which for the first time tallies butterfly data from more than 76,000 surveys across the continental United States.
The results: between 2000 and 2020, total butterfly abundance fell by 22 per cent across the 554 species counted. That means that for every five individual butterflies within the contiguous US in the year 2000, there were only four in 2020.
"Action must be taken," said Elise Zipkin, a Red Cedar Distinguished Professor of quantitative ecology at Michigan State University and a co-author of the paper.
"To lose 22 percent of butterflies across the continental U.S. in just two decades is distressing and shows a clear need for broad-scale conservation interventions," Elise added.
In this paper, Zipkin and Haddad were among a working group of scientists with the USGS Powell Center for Analysis and Synthesis who aggregated decades of butterfly data from 35 monitor programs, including records of over 12.6 million butterflies.
Using data integration approaches, the team examined how butterfly abundances changed regionally and individually for the 342 species with enough data.
Abundance is a term that threatens to become ironic. Butterfly populations dropped an average of 1.3% annually across the country, except for the Pacific Northwest. But even that encouraging result came with a caveat.
Further scrutiny of the apparent 10% increase in overall abundance in the Pacific Northwest over the 20-year study period was credited largely to the California tortoiseshell butterfly, which was enjoying a population boom not expected to be sustained.
"This is the definitive study of butterflies in the U.S.," said Collin Edwards, the study's lead author. "For those who were not already aware of insect declines, this should be a wake-up call. We urgently need both local- and national-scale conservation efforts to support butterflies and other insects. We have never had as clear and compelling a picture of butterfly declines as we do now."
Edwards had been a postdoctoral research associate at Washington State University, Vancouver, and now works at the Washington Department of Fish and Wildlife.
The results reveal that 13 times as many species declined as increased- with 107 species losing more than half their populations.
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