BY SANJNA PARULEKAR AND RASHMI GUTTAL.

The dark Italian rye grass, a short weed brought by the Spanish more than 200 years ago, stands prominently among the light-colored native plants on Tulare Hill in South San Jose.

Scientists believe that the grass, fed by nitrogen from the city's polluted air, has choked both the Goldfield and Purple Owl's Clover, the flowering wild plants favored as a food and home of the endangered Bay Checkerspot Butterfly. As the flowers have disappeared, engulfed by rye grass and other non-native plants, so have the butterflies. 

Late last month, the Silicon Valley Land Conservancy brought 40 cows to Tulare Hill to help bring back the native plants. The organization, which owns much of the hill, says it hopes the cows eat the dominant foreign grasses, leaving room for the native plants to grow and create a sustainable home for the endangered butterfly.

"In '07 and '08 there was only one butterfly found each year," said Craige Edgerton of the Silicon Valley Land Conservancy. "There are normally (8,000) to 10,000 butterflies in the area; that is why this program is so crucial."

Justin Fields, 36, a fourth-generation farmer, owns the cattle that are being used for this program. His family has roots in the Coyote Valley that trace back to 1914. Fields' great-great-grandfather bought the ranch in 1914, and the land was split among three siblings in the Ramelli family. Later, the land was further divided and is now separated by Highway 101 and train tracks.

Fields and his 7-year-old daughter, Jenna, herded the cattle on Tulare Hill. They were accompanied by their horses, Bailey and Buckwheat, their dog, Snip, and a random goat that seems to think he's part of the newly relocated cow herd.

"It just kind of fell in my lap," said Fields, explaining how he became interested in the butterflies after meeting conservation biologist Stuart Weiss, who wrote a study, "Scars, cows, and Checkerspot Butterflies: preserving the serpentine ecosystem in Santa Clara County."

Weiss has studied the serpentine rock ecosystem in San Jose and the effect of nitrogen oxide emissions from cars on the environment. He believes that by using cows to eat the non-native grasses, they can help bring back the population of butterflies on Tulare Hill. In the past studies, Weiss observed that in areas where cows grazed, native plants grew attracting the butterflies. In fields that were ungrazed, there were few checkerspot butterflies.

These butterflies, a checkerboard of red and orange spots, have been listed as a threatened species since 1987 because their habitat is slowly being destroyed. Among the many grasses that exist on the hill, the Checkerspot Butterfly is the most dependent on Plantango Erecta, a plant that is being choked by foreign grasses such as the Italian rye grass.

The butterflies lay eggs in the plants, and the plants, in turn, shelter the cocoons. Because of the overgrowth of foreign grasses in the area, the native plants are becoming more scarce, consequently putting the Checkerspot Butterfly at a greater risk of endangerment.

As the cows munched on rye grasses, conservancy officials observed quietly. A sheep dog herded the cows. In four years, they hope the Checkerspot Butterfly will be back on Tulare Hill.