By Tracy Correa
On a sunny day earlier this month, a small group gathered and gingerly released caterpillars and butterflies into an open field in Santa Clara County’s Tulare Hill area.
It was a low-key, but momentous event. This was the long-awaited release of the threatened Bay checkerspot butterfly and its pre-butterfly stage caterpillar or larvae on land that includes property owned by PG&E.
On March 1, 60 of the Bay checkerspot butterflies were released and 100 black, orange-spotted caterpillars — that will one day become the butterflies — were carefully collected from nearby Coyote Ridge and placed at the Tulare Hill site. In the days leading up to this, 4,900 of the caterpillars were moved to Tulare Hill in the San Jose area.
Few people understand the historic release better than Craige Edgerton, executive director of the Silicon Valley Land Conservancy. Edgerton took part in the butterfly release that also included PG&E’s Andi Henke, a senior wildlife biologist, Dr. Stuart Weiss from Creekside Science and Terry Mahoney, with Calpine Inc.
“This was a big deal,” said Edgerton, who struggles to find the right words to explain just how big. “The habitat is now finally in good enough shape for these butterflies,” he said.
Bay butterfly population was threatened
The Tulare Hill area was historically grazed until 2001. The grazing halt led to the proliferation of non-native grass, which chokes out the native forbs and nectar species necessary for the butterfly to flourish.
In 2003, the Calpine Corporation dedicated 116 acres of Tulare Hill (about one-third of the entire property) to the Silicon Valley Conservancy as a preserve for the butterfly, which was designated as threatened under the federal Endangered Species Act in 1987.
PG&E, which also owns property adjacent to Tulare Hill, secured a Safe Harbor Agreement with U.S. Fish & Wildlife Service that allowed it to continue operating its transmission lines while committing to help in the Bay checkerspot butterfly conservation effort. The area is home to a critical power line corridor consisting of five transmission lines in Santa Clara County.
A strategic grazing program on PG&E’s acreage was initiated in 2008 — in partnership with the Silicon Valley Land Conservancy – to control the non-native plants and allow the butterfly’s host plant, dwarf plantain, as well as other native nectar producing plants and the listed Santa Clara Valley Dudleya more opportunity to grow.
Carefully planned reintroduction
Edgerton said all of the committed parties have been working toward the release of the butterflies and caterpillars.
“Now the flowering forbs have returned. We hope we have sufficient numbers for the butterflies,” he said.
PG&E’s Henke said collecting the caterpillars and butterflies and placing them on Tulare Hill was a fun and rewarding experience. “It’s great to be able to support cooperative efforts to restore a threatened species,” she said.
However, Henke said the release is only part of a multi-stage approach to help the Bay checkerspot butterfly. “Planned monitoring efforts will track the translocated population and it’s anticipated that this effort will help ensure the threatened butterfly’s survival.”
About half the planned releases took place on Calpine property and the other half on PG&E’s property. The Santa Clara County Department of Parks and Recreation, which owns the northern half of Tulare Hill, helped in the collection phase of the program.
Those involved in the Bay checkerspot conservation effort say that it’s important that the entire hill be populated with the butterfly to help ensure its long-term survival. They also point to the conservation project as a great example of nonprofits, the scientific community, business and government working together to protect a threatened species and preserve rare serpentine grassland in the Bay Area.
PG&E has been recognized for its wildlife conservation efforts, including its work to protect the Bay checkerspot butterfly. In 2011, PG&E partnered with the land conservancy to seek formal recognition from the Wildlife Habitat Council (WHC) for its efforts to enhance habitat as part of WHC’s “Wildlife at Work” accreditation program.
E-mail Tracy Correa at Tracy.Correa@pge.com.