Drier, Warmer American West Marks 40-Year Butterfly Decline

The decades-long decline in butterfly populations across U.S. western states has researchers calling for improvement and expansion of habitat conservation methods.

Butterfly decline was estimated using data from 72 locations with at least 10 years of data per location and more than 250 butterfly species, including this Adelpha bredowii, or California Sister. (Credit: Chris Halsch, University of Nevada, Reno)

(CN) — The American West is in the grips of a consistent 40-year decline in butterfly populations, a trend researchers on Thursday said can be culled using expanded conservation as climate change makes the region increasingly drier and warmer.

Butterfly populations across the western United States have declined 1.6% annually over the last four decades, according to the study published Thursday in the journal Science.

That figure mirrors rates of decline for other insect populations around the world, the study said.

A team of University of Nevada, Reno-based researchers set out to analyze the decline of butterfly populations across relatively arid, undeveloped areas of the West, as opposed to previous studies which focused on more developed, densely-populated regions. 

Researchers and volunteer citizen scientists closely examined butterfly populations across 70 sections of the region, gathering an average of 10 years of data per site on over 250 species.

The team also considered the impact of land use policies and the rates of climate change for each regional section.

The data — which represent butterfly species populating western U.S. states between 1977 and 2018 — revealed that butterfly species decline is attributed to autumn months that are made increasingly warmer by climate change.

Instead of focusing on a single butterfly species, the findings suggest grouping conservation efforts based on species’ shared habitats or host plant preferences.

Study co-author Katy Prudic of the University of Arizona said in a statement released with the study that understanding each region’s annual climate will supplement the tailored approach to conservation. 

“Western butterfly declines are associated with increasing fall temperatures across the U.S. wildlands,” Prudic said. “Conservation, management and restoration on public lands, especially along cooler riparian areas, will be critical for preventing butterfly declines and extinction.”

Researchers wrote in the study that legal protections for open spaces and public lands won’t be sufficient for species protection without understanding the impact climate change is having on the region.

Lead author of the study, University of Nevada, Reno biology professor Matt Forister, said in the statement the findings underscore the need for conservation based on an understanding of the region.

The American West contains verdant forests, arid deserts, lush coastline and some of the most populous U.S. urban areas and understanding climate change’s impact on them is critical, Forister said.

“The fact that declines are observed across the undeveloped spaces of the western U.S. means that we cannot assume that insects are okay out there far from direct human influence,” Forister said. “And that’s because the influence of climate change is, of course, not geographically restricted.”

Forister added that the findings show the importance of expanding butterfly habitat restoration projects, especially since butterflies are part of the pollinator network that is critical for the world’s food systems.

“The widespread butterfly declines highlight the importance of careful management of the lands that we do have control over, including our own backyards where we should use fewer pesticides and choose plants for landscapes that benefit local insects,” Forister said in the statement.

Researchers did not immediately respond to a request for further comment on the study.

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