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How butterflies are regenerating San Francisco's sand dunes

Silvery Blue and Xerces Blue share the same host plant: deerweed (Acmispon glaber). Pictured in UCSC’s Fort Ord Natural Reserve. Photo credit: Gayle Laird.

On April 11, 2024, the California Academy of Sciences released 28 Silvery Blue butterflies in the Presidio, using the power of community-driven science to repair local ecosystems. Together, scientists and environmental organizations such as the Presidio Trust, Creekside Science and Revive & Restore are introducing an ecological replacement for the Xerces Blue butterfly, which went extinct in 1941. By bringing back a similar species to perform the same functions in the ecosystem as the Xerces Blue, the Cal Academy hopes to increase biodiversity and strengthen the ecosystem’s resilience to human-made changes to the environment.

According to Chris Grinter, collection manager of entomology at the Cal Academy, San Francisco’s sand dunes, ranging from Ocean Beach to Telegraph Hill, housed over 40 species of butterflies in the 19th century. With the rapid development of coastal neighborhoods in the latter half of the century, many of these butterfly species lost their native habitats and were ultimately driven to extinction. 

In 2006, the Presidio Trust, National Park Service and Golden Gate National Parks Conservancy began their efforts to restore ecosystems and increase biodiversity in the Presidio. The Presidio is now considered a biodiversity hotspot in the San Francisco Bay Area. But one element inhibits the habitat from full restoration: the absence of the Xerces Blue butterfly of the gossamer-wing family, with its critical role as a pollinator and deerweed-consuming member of the food web.

Initially discovered in 1852, the Xerces Blue butterfly was the first butterfly species in the United States to become extinct as a result of human-made disturbance and habitat loss. 

“The Xerces project is super unique because Xerces is our poster child of how we failed — they went extinct specifically because we removed their habitat,” said Durrell Kapan, PhD,  senior research fellow and project lead at the Cal Academy, in an interview.

To restore the roles the Xerces Blue played in the Presidio ecosystem, the Cal Academy is utilizing its collection of 46 million scientific specimens to analyze the butterfly’s genome. They use this data to compare the genome to nearby populations of Silvery Blue butterflies, the closest living relative of the Xerces Blue, to replace the extinct Xerces in San Francisco.  

“We were able to use information from the past — our collections — to help us chart a way forward for these new [ecosystems], … [which] aligns with what the Academy is trying to do … to regenerate or restore these natural systems that have gone extinct,” said Shannon Bennett, PhD, chief of science at the Cal Academy, in an interview.

To find a successful replacement, Kapan and his team searched for a nearby population of Silvery Blue Butterflies that shared Xerces’ host plant, deerweed, as well as environmental preferences. The Cal Academy researchers found a close matching group living in Monterey.

“We started with genetics and then we went to ecology, and … looked at the places around [the San Francisco Bay Area] and said, ‘Are there any thriving populations of butterflies that have those characteristics that are predicted?’ And indeed there were,” said Kapan.

Kapan and his team conducted a trial release of 15 butterflies to test the team’s release method and the butterflies’ environmental acclimation. Following the trial release, the scientists returned to Fort Ord Natural Reserve and Garrapata State Park a week later to gather more Silvery Blues. After feeding the butterflies Q-Tips soaked in fruit punch-flavored Gatorade to sustain the butterflies throughout their day-long journey, the Cal Academy, with the assistance of other organizations, introduced 28 more Silvery Blue butterflies to the Presidio on April 11, 2024.

“By bringing back those butterflies, it's kind of like telling ourselves, ‘Yes, we can, we can fix things,’” said Kapan. “[And] it's just the first step. There are many, many, many more species that have suffered similar, if not completely identical fates to Xerces.”

The butterflies are a testament to the importance of community-led habitat restoration and a beacon of hope for the future of San Francisco’s ecosystems. 

“[There is] the ecological piece of it, but I also recognize that there's a really important … social and cultural piece, which is that … restoring of a lost component,” said Phoebe Parker-Shames, PhD, wildlife ecologist with the Presidio Trust, in an interview. “[The introduction of Silvery Blues] feels like one of those small ways in which we try to cope with the mass extinctions that we have happening in the world.”

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