Bay Checkerspot Butterfly

(Left): Caption from Washington Post: Traffic-induced habitat changes are threatening the breeding grounds of the bay checkerspot. (Courtesy Jon Christensen)


There is an article in today's Sacramento Bee, written by Juliet Eilperin from the Washington Post, discussing the rare Bay Checkerspot Butterfly, which lives on endangered habitat in the Serpentine Hills immediately adjacent to San Jose, and on Coyote Ridge, south of town.

Recently, a biologist named Stuart Weiss determined that cattle grazing is an essential element in keeping the Checkerspot's favored shrubby habitat from being overrun by nitrogen-loving grasses. Nitrogen deposition (nitrogen-bearing air-pollutant compounds like nitric acid and ammonia settling out on the land) has greatly increased in recent decades as the area became urbanized. Nitrogen deposition tilts the biological playing field towards grasses and away from shrubs. Grass-eating cows tilt the playing field back in the other direction, back towards butterfly-friendly shrubs.

But on Coyote Ridge's northern edge, their numbers crashed in the early 1990s as Silicon Valley's high-tech boom spurred a wave of development. The species, with its brilliant orange-and-red-flecked wings, first crashed between Palo Alto and San Francisco in the 1980s, prompting federal officials to list it as threatened with extinction. Then in the early '90s its numbers dropped on the southern edge of San Jose, around the suburban subdivisions that abut Coyote Ridge.

The cause was a mystery until conservation biologist Stuart Weiss figured out that the butterfly's woes stemmed from a combination of pollution from the freeway below and, surprisingly, a cutback in local cattle grazing.

The fate of the bay checkerspot -- despite its problems, the butterfly still hatches in mid-April -- highlights the complexity of ecological relationships. As development surged, the stress of vehicular and power plant pollution devastated a population cycle that had existed for centuries.

Over years of research, Weiss -- who has worked for utility and waste management companies as well as conservation groups and government agencies -- documented how the nitrogen oxide emissions from cars commuting to Silicon Valley enriched the nutrient-poor serpentine-rock soil that sustains the native grasslands on Coyote Ridge. This soil enrichment allowed invasive grasses -- which flourish in more nitrogen-rich soil -- to out-compete the native plants on which the checkerspot depends. When local ranchers stopped grazing their cows on one side of the ridge, it made things worse, because grazing helped keep invasive grasses in check.

"The grazed side is great butterfly habitat, the ungrazed side is lousy," Weiss said. "You end grazing in the areas and it's bye-bye butterflies."

While Weiss may appear an unlikely champion for ranchers -- the amiable Stanford-trained scientist brings along a thermos of green tea and Ghirardelli bittersweet chocolate on his field trips -- he says that, in this case, cows play a vital role in preventing what he calls a "drive-by extinction." Cattle seek out the most nutritious grasses, he explained, and so they consume the grasses that threaten the dwarf plantain (Plantago erecta), critical to the checkerspot caterpillars.

There is no question that exhaust from cars cruising below Coyote Ridge is depositing nitrogen in the ridge's soil. About 110,000 vehicles a day traverse Highway 101 and, along with other urban sources, annually deposit 15 to 20 pounds of nitrogen per acre on the ridge, according to Weiss's monitoring equipment. Some of the nitrogen is absorbed by living plants, while small particles of the pollutant stick to plants and the ground and are washed into the soil by rain. By contrast, pollution from power plants and vehicles each year deposits just four to five pounds of nitrogen per acre on Jasper Ridge, a Stanford University biological reserve half an hour away.

By the mid-1990s, the checkerspot's numbers on Coyote Ridge's northern end had dropped from about 50,000 to near extinction. But in areas that have been grazed and well maintained, the population hovers in the low hundreds of thousands.

As part of the state permitting process for construction of the recently-built and nitrogen-generating Metcalf power plant, Calpine Corporation agreed to set up an endowment to ensure that cattle grazing can be implemented in perpetuity on these hills, whatever the cattle market might be, in order to offset the extra nitrogen deposition from the power plant, plus the far-larger nitrogen deposition wafting in from automobile emissions.

Unlike some conservation sagas, however, in this case local businesses and elected officials listened to Weiss, and it has made a difference, not only on Coyote Ridge. When Calpine Corp. decided to build a 600-megawatt power plant that would emit 120 tons of nitrogen oxide a year, Weiss lobbied the firm to create a 131-acre butterfly and plant reserve on nearby Tulare Hill as mitigation.

Calpine assented, setting aside the habitat six years ago and providing a $1.3 million endowment to manage the land. "It was increasingly clear there was some concern about sensitive hillside habitat, and this seemed to be the best means to address this," said Kent Robertson, Calpine's director of public relations. Local chapters of the Sierra Club and American Lung Association welcomed the move, he said.

That established a precedent, so when the Santa Clara Valley Transportation Authority moved to expand Highway 101 below Coyote Ridge from four lanes to eight, the U.S. Fish and Wildlife Service instructed the agency to preserve 548 acres of habitat as compensation. Fish and Wildlife determined that the pollution from the increased traffic posed a threat not only to the butterfly but to four federally listed endangered plants as well: the Santa Clara Valley dudleya, Metcalf Canyon jewelflower, coyote ceanothus and Tiberon paintbrush.

"Obviously, when you are expanding a highway or doing a major construction project, there are going to be environmental impacts," said transportation agency spokeswoman Jayme Kunz, adding that the June 2005 land purchase cost $55.3 million. "We felt mitigation was a critical part of doing any kind of construction that would expand our highway."

In any event, as part of my job here at Sierra Research, I did the air quality modeling regarding nitrogen deposition on these hills, on behalf of Calpine Corporation.

Long live the Checkerspot Butterfly!