Mission Blues [Western USA]

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By Bruce Byers

Bruce is an ecologist, writer, and independent consultant. He is currently writing a book of creative nonfiction nature essays about the Golden Gate Biosphere Reserve in California, from which this story is adapted.

A breeze was just starting up as we parked along Quarry Road in Brisbane, California, on the eastern slope of San Bruno Mountain. I tagged along with a local butterfly conservation scientist and a two-person team from the Golden Gate National Recreation Area. Mission of the day: to capture and translocate some endangered Mission Blue butterflies from this area to Sweeney Ridge. The motive was to re-establish another population of Mission Blues there, which would theoretically reduce their vulnerability to factors that might cause them to disappear from San Bruno Mountain, and thereby enhance their long-term survival.

The translocation project was being conducted with the permission and blessing of the U.S. Fish and Wildlife Service (USFWS), which has the responsibility and authority for safeguarding the Mission Blue and other species listed under the Endangered Species Act. This year was the first year of translocations from San Bruno to Sweeney Ridge, and the USFWS-approved plan was to relocate 60 butterflies to re-establish the population there.

We scoured the steep hillside grassland, focusing on clusters of lupines, where Mission Blue females might be hanging out and males might be patrolling in the hope of mating. Quick and elusive, flying low in the rising wind, the males gave a flash of blue upper wings in just the right light; the females looked browner.

A member of the translocation team looking for Mission Blues

Spotting tiny Mission Blues, with a wingspan the size of a quarter, was obviously a skill acquired after considerable experience, and I was a novice. The translocation team was under a strict protocol from the USFWS. Only six females and two males could be taken in this area today, a small fraction of the estimated local population. After a few hours of searching, the authorized sample had been captured in nets swooped over the lupines and carefully coached into tiny plastic containers, and we descended to our cars.

A Mission Blue male ready for translocation

The butterfly subfamily Polyommatinae, called the “blues” by lepidopterists, is one of the most diverse groups of butterflies in North America. They seem to have found an evolutionary mechanism for adapting to local environments and forming new subspecies and species to a greater extent than most other groups of butterflies, according to recent high-powered genomic research. The Mission Blue, Icaricia icarioides missionensis, a subspecies of a butterfly called Boisduval’s Blue, apparently used this evolutionary trick to adapt to the coastal grasslands of the San Francisco Peninsula and the Marin Headlands just across the Golden Gate.

When a party from the Spanish exploring expedition led by Gaspar de Portolá climbed the coastal hills west of what is now the San Francisco suburb of Pacifica on November 4, 1769, Europeans saw San Francisco Bay for the first time. The place is now called Sweeney Ridge, and it is part of the Golden Gate National Recreation Area, managed by the National Park Service. The Spaniards did not “discover” the Bay, of course: native Ohlone and Miwok people had been living around it for thousands of years. Soon after the Portolá expedition, in 1776, a mission named after Saint Francis of Assisi was established. The scientific and common names of this unique butterfly refer to the fact that it was first collected near this old mission. From the point-of-view of the endangered Mission Blue, the association with Saint Francis—whose reputed love of animals and nature has led some to call him the patron saint of animals—is ironic.

The habitat of the Mission Blue would have been much more extensive two-and-a-half centuries ago. Indian use of fire held woody chaparral and coastal sage scrub vegetation in check and favored the grasslands where the butterfly’s lupine host plants occur. Residential and industrial development severely reduced and fragmented the coastal grasslands after World War II, and the Mission Blue population plummeted. It was listed as “endangered” under the Endangered Species Act in 1976.

Three species of perennial lupines, on which it lays its eggs and its larvae feed, are important to its survival: silver lupine (Lupinus albifrons), summer lupine (L. formosus), and varied lupine (L. variicolor). All three occur on San Bruno Mountain, the last best piece of coastal grassland in the Bay area, which supports the largest population of Mission Blues. The silver lupine is most common and most-used as a host plant; but it is probably the diversity of lupines, and the ability of the Mission Blue to use all three species, that underlies the ecological resilience that has allowed it to persist.

Silver lupine (Lupinus albifrons), a host plant of the Mission Blue

A 1982 study found that Mission Blues could fly about a quarter of a mile between patches of their grassland habitat. On their own, they probably can’t reach other “islands” of suitable habitat that still exist near San Bruno Mountain, such as Sweeney Ridge, five miles away as the butterfly flies. Mission Blues were observed there in the late 1980s, but then they disappeared. And so begins this “rewilding” story.

For many people, the term “rewilding” evokes reintroducing large carnivores and creating connecting corridors of habitat so that they can again roam through wilderness ecosystems at regional or even continental scales. They picture wolves, grizzlies, mountain lions, jaguars… But that definition is too narrow. 

From the point-of-view of the Mission Blue, these remnant patches of grassland and lupines in the San Francisco suburbs are their world, their continent, their wilderness. The skyscrapers of San Francisco are visible, communications towers command the hilltops, powerlines crisscross the ridges, and suburbs of ticky-tacky houses and roaring freeways hem in these small remnant grasslands, which have improbably—only because of the inspiring activism and work of local conservationists over more than half a century—been protected from all that human infrastructure development. These grasslands may not look wild to our eyes, but they would if we saw them through the eyes of butterflies.

From San Bruno Mountain, with the captives chilling in a cooler to keep them comfortable and calm, we drove south on the Bayshore Freeway, then west toward Skyline College; we parked in an upper parking lot and used a shortcut-trail to Sweeney Ridge. When we arrived at the release site in the early afternoon, the wind was up. In this area, the National Park Service and volunteers from the Golden Gate National Parks Conservancy have been planting more of the silver lupines that are the Mission Blue’s preferred host plant. Big squares of tulle-fabric netting were spread over clumps of re-established lupines and held down with rocks. Butterflies we captured a few hours earlier on San Bruno Mountain were released from the tiny plastic containers under these protective shrouds, and offered snacks of sugar-water-soaked cotton balls. Within a short time, some females were laying eggs on the lupines in their new home.

A Mission Blue female under netting after translocation to Sweeney Ridge

Can even small stories of resilience and rewilding, like this one about the Mission Blue, help us rewild our human hearts and spirits and motivate us to work toward a future where all species can thrive together?

Location of Sweeney Ridge