How Drought Affected Northern California’s Butterflies

by Greg Watry | June 13, 2018

Using nearly 45 years of butterfly population field data, a study published in Climate Change Responses reveals how recent record-setting temperatures and drought conditions affected butterfly populations at various elevations in Northern California.

Researchers from UC Davis, University of Nevada, Reno, University of Tennessee, Knoxville, and Texas State University found that the number of butterfly species and individuals observed per year increased at lower elevations during the 2011-2015 California drought but decreased at higher elevations.

“Counter to intuition, butterfly faunas near sea level apparently benefited from the drought, temporarily reversing long-term declines, while montane Sierran faunas were severely harmed,” said Distinguished Professor Arthur Shapiro, Department of Evolution and Ecology.

The study’s results also raise questions about the methods researchers use to predict how climate change will impact species. “What our study demonstrates is that our imaginations are not very good in terms of projecting how things are going to react,” Shapiro said.

A gulf fritillary, or passion butterfly, visits a cosmo flower. (Kathy Keatley Garvey/UC Davis)

Unexpected effects of the millennium drought

Over the course of the study, researchers visited 10 different sites spread between the coast and the Sierra Nevada, collecting population data from 163 butterfly species. Since the mid-1990s, butterfly populations at the study’s lowest elevation sites—which included sites in the Central Valley—were in a decline, while butterfly populations at high elevations sites remained relatively stable.

Then the 2011-2015 drought hit.

During the so-called millennium drought, butterflies at the low elevation sites experienced some of the most productive years in nearly two decades, increasing in both number of individuals and number of species. At high elevation sites, the effect was opposite, with number of species and individuals declining during the drought.

Gulf fritillary butterflies mating. (Kathy Keatley Garvey/UC Davis)

We have lost species on a regional basis and these didn’t come back, but the species that were still around ended up doing much better in the drought
– Arthur Shapiro

Shapiro cautioned that the study’s results don’t necessarily mean butterfly populations are rebounding in the long-term at low elevations.      

“We have lost species on a regional basis and these didn’t come back, but the species that were still around ended up doing much better in the drought,” Shapiro said.

Learn more about this research in a longer version of this article at the UC Davis College of Biological Sciences’ website.



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