Scientists, rangers, and park supporters have taken another step to bring back Bay checkerspot butterflies to their historic home at Edgewood County Park and Natural Preserve in Redwood City.
The butterflies suffered local extinction in 2002 due to a decrease in the number of their host plant, dwarf plantain. Ecologist Dr. Stuart B. Weiss called it “drive-by extinction” when his research showed how exhaust fumes (nitrous oxides and ammonia) from cars driving on nearby Interstate 280 fertilize nonnative grasses, allowing them to drive out native wildflowers that support the butterflies.
Edgewood is now being restored through a rotational mowing program, and checkerspot host plant and nectar sources are abundant in the area once again. With adequate habitat in place, the US Fish and Wildlife Service granted a permit to transfer butterflies, in both the caterpillar and adult form, from a healthy population at Coyote Ridge to 15 acres of prime habitat at Edgewood.
An effort in 2007 was unsuccessful due to very dry weather and a small number of transferred caterpillars. While this was a setback, mowing continued to keep the site ready for the eventual butterfly homecoming. In February 2011, more than 4,000 caterpillars were introduced. About 130 adults were counted by volunteer monitors during the flight season (March and April 2011), and about 2,000 caterpillars, offspring of those butterflies, were noted this winter. To further the odds of firmly reestablishing this species, another 4,852 caterpillars were introduced in February 2012.
Butterflies judge habitat quality by the presence of other butterflies. They need critical mass to settle down and develop a sedentary tendency. Introducing too few butterflies may increase the likelihood that they will fly away looking for other individuals. More than 100 butterflies have been spotted already this year, a strong indicator of success.
To further increase the likelihood of success, additional adults were introduced on April 3, 2012. The larvae were reintroduced into their historic home, in the serpentine grassland between the serpentine loop and the clarkia trails. The site can be observed from the serpentine loop, facing the freeway, and looking across the swale and upslope. The site is protected and not crossed by public trails.
“An added benefit of the restoration is that the native carpets of wildflowers have been restored,” said Ranger John Trewin. “We ask people to stay on trails to protect the sensitive habitat, but the views from those trails are spectacular. One day when the butterfly population multiplies and has a chance to reestablish itself over the next few seasons, visitors may be able to see adult butterflies fluttering about.”
Partners of the San Mateo County Parks include: Creekside Center for Earth Observation San Mateo County Parks Foundation, US Fish and Wildlife Service, Pacific Gas & Electric Company, the Jiji Foundation, and the Friends of Edgewood.