Pacific Southwest Region
California, Nevada and Klamath Basin

Service Finds Thorne’s Hairstreak Butterfly Does Not Warrant Protection Under the Endangered Species Act

Feb 22, 2011

February 22, 2011

Contact: Stephanie Weagley, U.S. Fish and Wildlife Service
Phone: (760)431-9440 ext. 210, Email:

U.S. Fish and Wildlife Service Finds Thorne’s Hairstreak Butterfly
Does Not Warrant Protection Under the Endangered Species Act

CARLSBAD, CA - The U.S. Fish and Wildlife Service (Service) announced today it has completed a 12-month finding on a petition to list Thorne’s hairstreak butterfly (Callophrys [Mitoura] grynea thornei) under the Endangered Species Act. After an in-depth status review, we find that listing Thorne’s hairstreak butterfly as threatened or endangered is not warranted at this time.

In 2004, the Service received a petition from the Center for Biological Diversity and David Hogan to list the species and determined in a 2006 finding that the petition did not present substantial scientific information to indicate listing the butterfly might be warranted. A settlement agreement was reached in October 2009, whereby we agreed to review the petition again and look at any new information about the butterfly and its habitat that has since become available. On April 5, 2010, we determined in the new 90-day finding that listing Thorne’s hairstreak butterfly may be warranted.

Recent surveys (post-2003 and 2007 fires) reveal that Thorne’s hairstreak butterfly’s current known range is greater in size than its known historical range. The butterfly now occupies several locations in the southwest quadrant of Otay Mountain that were not previously known. Additionally, a newly colonized butterfly location was discovered in 2010 in recently created habitat within the Otay River Valley.

Throughout the areas within the 2003 and 2007 fire perimeters, Tecate cypress regrowth and butterflies were observed in the majority of the habitat post-fire. This indicates that the butterfly is relatively resilient to fire impacts because it can recolonize burned areas, and in some cases persist within mapped fire perimeters. Furthermore, recent butterfly observations in created habitat within the Otay River Valley indicate this butterfly can move fairly considerable distances and colonize new stands of Tecate cypress at lower elevations. 

Over 95 percent of the butterfly’s habitat is currently conserved and managed with the majority of habitat covered by the BLM Otay Mountain Wilderness and the County of San Diego Subarea Plan under the Multiple Species Conservation Program. Additionally, we have no evidence supporting declines in the butterfly’s range or abundance throughout its known distribution.

Although climate change and fire frequency predictions indicate the butterfly’s habitat could decline long-term, it is not clear this will occur, nor that direct or indirect effects of climate change would cause the butterfly’s range or abundance to decline substantially.

The Service anticipates current management efforts will continue with our conservation partners and we will continue to actively engage the public and others in the search for improved and innovative ways to conserve and protect species and their habitats. 

Thorne’s hairstreak butterfly has rich reddish brown wings with dark brown shading and is found exclusively in the Otay Mountain area in southern San Diego County, California. The butterfly is closely associated with Tecate cypress forest intermixed with chaparral and lays its eggs only on the larval host plant Tecate cypress to complete its life cycle. Adults are known to feed on a variety of nectar sources, including California buckwheat, Ramona lilac, deerweed, and narrowleaf milkweed.

A copy of the 12-month finding can be viewed online today at the Federal Register Public Inspection Page. The official copy will be posted on February 23, 2011 at at Docket No. FWS-R8-ES-2010-0016. Please submit any new information, materials, comments, or questions concerning this finding to the Carlsbad Fish and Wildlife Office. The mission of the U.S. Fish and Wildlife Service is working with others to conserve, protect and enhance fish, wildlife, plants and their habitats for the continuing benefit of the American people. We are both a leader and trusted partner in fish and wildlife conservation, known for our scientific excellence, stewardship of lands and natural resources, dedicated professionals and commitment to public service. For more information on our work and the people who make it happen, visit