Study documents declines across hundreds of species over recent decades, and finds years featuring warmer, drier autumns are particularly deadly
By Alex Fox
MARCH 9, 2021
Butterflies are in decline across the American West as climate change makes the region hotter and drier, reports Dino Grandoni for the Washington Post.
The new research, published last week in the journal Science, details winnowing butterfly populations across the majority of the 450 species evaluated by the researchers.
By combining decades of butterfly sighting data recorded by scientists and amateurs, the team found that the total number of butterflies observed west of the Rocky Mountains has fallen by 1.6 percent every year since 1977.
“You extrapolate it and it feels crazy but it’s consistent with the anecdotal ‘windshield effect’ where people aren’t spending time cleaning insects from their car windshields anymore,” Matt Forister, biologist at the University of Nevada and the study’s lead author, tells Oliver Milman of the Guardian. “Certainly many butterfly species are becoming so rare it’s hard for some people to see what were once widespread, common species.”
In particular, the iconic western monarch butterfly’s population has crashed to the tune of 99.9 percent, reports Liz Langley for National Geographic. But, per National Geographic, the declines have also pushed less famous species such as the Boisduval’s blue and the California dogface butterfly, California’s state insect, to the brink of extinction.
“The influence of climate change is driving those declines, which makes sense because they’re so widespread,” Forister tells the Post. “It has to be something geographically pervasive.”
To reach their troubling findings, the researchers combined databases of butterfly counts conducted by scientists and amateur insect enthusiasts at 72 locations in the western U.S. To zero-in on the contribution of climate change, the researchers made sure to include locations that were relatively undisturbed by agriculture and human development to limit the influence of other threats to butterflies such as habitat loss and pesticides.
Even in these nearly pristine locations, butterflies were still disappearing.
“This is one of the first global cases of declines occurring in wildlands, away from densely populated human-dominated landscapes, and the rate of 1.6 percent is calamitous,” David Wagner, an ecologist at the University of Connecticut who was not involved in the research, tells the Post.
In particular, Forister tells National Geographic his team’s analysis found that warmer fall seasons appeared to be deadliest for butterflies. “We’ve been really focused on the [warming of] spring for a couple of decades now,” Forister tells National Geographic. However, he adds, “warming at the end of the season is a really negative impact.”
The study doesn’t pinpoint exactly what about the warmer, drier conditions created by climate change is laying the butterflies low. Per the Guardian, it could be that longer, more intense summers are leaving plants parched, which diminishes the supply of the nectar the butterflies feed on. Warmer winters might also somehow interfere with the hibernation-like state butterflies enter during the colder months, leaving them weaker come spring.
“The declines are extremely concerning ecologically,” Dara Satterfield, a butterfly researcher at the Smithsonian Conservation Biology Institute who was not involved in the study, tells the Guardian. “We know butterflies and moths act as pollinators, decomposers, nutrient-transport vessels, and food sources for birds and other wildlife.”
This latest study is the most recent in a series of research papers documenting declining insect populations across the globe. Speaking with Melissa Sevigny of radio station KNAU, Forister says the lesson from this research may be that “if butterflies are suffering out there in protected areas, counterintuitively, that elevates the importance of land closer at hand,” he says “You could think twice about spraying poisons in your background, because our backyards are good butterfly habitat.”
Alex Fox is a freelance science journalist based in Washington, D.C. He has written for Science, Nature, Science News, the San Jose Mercury News, and Mongabay. You can find him at Alexfoxscience.com.Read more from this author | Follow @Alex_M_Fox
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