Conserving the Nature of America

News Release

Critical Habitat Designated for Bay Checkerspot Butterfly

August 26, 2008


Division of Public Affairs
External Affairs
Telephone: 703-358-2220

Action expected to have minimal additional cost to public

The U.S. Fish and Wildlife Service (Service) today designated 18,293 acres in Santa Clara and San Mateo counties as critical habitat for the beautiful but threatened Bay checkerspot butterfly, a species that occurs only on small patches of inhospitable soil where its limited food supply grows.

Santa Clara County has 16,601 acres of the critical habitat, or 90 per cent. In Santa Clara County more than 10,000 acres of critical habitat are in the hills east of Highway 101, extending about 15 miles from Yerba Buena Road to Anderson Lake. Another 6,000 acres are west of 101 in six smaller units extending south from the City of Santa Clara nearly to Highway 152.

In Santa Clara County, all of the critical habitat occurs in the area to be covered by a comprehensive Habitat Conservation Plan (HCP). Landowners, developers, environmental groups and eight local and state government agencies are cooperating in the planning effort. The HCP would protect important habitat for 30 listed and unlisted species over a 520,000-acre area, rather than focusing on a single species such as the Bay checkerspot. The Service believes that such voluntary efforts are more effective in protecting species and their habitat.

In San Mateo County four units are designated, totaling 1,692 acres: Jasper Ridge, Edgewood Park, Pulgas Ridge and San Bruno Mountain. Coincidentally, the Services first HCP, established on San Bruno Mountain in 1983, is currently being revised to provide a sustainable funding source. The revised HCP will cover the bay checkerspot, which was not listed under the federal Endangered Species Act (ESA) until 1987.

The annual costs directly associated with the bay checkerspot critical habitat will be minimal. They are estimated to be between zero and no more than $750,000 over the next 22 years, according to a required economic analysis prepared for the Service by a private consulting firm, Berkeley Economic Consulting.

The bay checkerspot butterfly is identifiable by its distinctive markings on its 2-inch wingspan. All its wing veins have black bands around bright orange, red and white spots. It lives in areas with serpentine soils, a harsh environment lacking many plant nutrients, notably nitrogen and calcium. This limits the butterflys original range to areas that support its only larval foods, dwarf plantain, plus two secondary food sources eaten by larvae when the plantain dies off, purple owls clover and exserted paintbrush.

Historically, the Bay checkerspot occurred primarily along the spine of the San Francisco peninsula, from Twin Peaks to southern Santa Clara County and in a few pockets in Alameda and Contra Costa counties. However, habitat loss and fragmentation, air pollution, pesticides, vehicle strikes, fire, overgrazing, gopher control, illegal collecting, and invasion of exotic grass species have greatly reduced the butterfly's numbers.

Critical habitat is a term in the ESA that identifies geographic areas containing features essential for the conservation of a threatened or endangered species and that may require special management considerations or protection. Designation of critical habitat is required by the ESA.

The designation of critical habitat does not affect land ownership or establish a refuge, wilderness, reserve, preserve or other conservation area. Federal agencies that undertake, fund or permit activities that may affect critical habitat are required to consult with the Service to ensure such actions do not harm critical habitat. The designation does not affect purely private or state actions on private or state lands, nor require non-federal lands to be positively managed for conservation.

This designation completes a court-ordered process that began when the Home Builders Association of Northern California challenged a 2001 designation of critical habitat for the species, contending that the Service had failed to analyze the economic impacts. In a 2006 settlement, the Service agreed to reissue the critical habitat.

The new designation is 5,610 acres smaller than the 2001 designation, and 1,453 acres smaller than the Services 2007 proposal for this new rule. The reduction is the result of identifying and removing from critical habitat areas that already are developed or are unsuitable for the butterfly, such as forests.

The critical habitat rule, along with other information about the Bay checkerspot is available on the Internet at and the Federal Register at:


The U.S. Fish and Wildlife Service is the principal Federal agency responsible for conserving, protecting and enhancing fish, wildlife and plants and their habitats for the continuing benefit of the American people. The Service manages the 97-million-acre National Wildlife Refuge System, which encompasses 548 national wildlife refuges, thousands of small wetlands and other special management areas. It also operates 69 national fish hatcheries, 64 Fish and Wildlife Management offices and 81 ecological services field stations. The agency enforces federal wildlife laws, administers the Endangered Species Act, manages migratory bird populations, restores nationally significant fisheries, conserves and restores wildlife habitat such as wetlands, and helps foreign and Native American tribal governments with their conservation efforts. It also oversees the Federal Assistance program, which distributes hundreds of millions of dollars in excise taxes on fishing and hunting equipment to state fish and wildlife agencies.  

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