Type: report

Article abstract: The Harbison's dun skipper (Euphyes vestris harbisoni) is a rare subspecies with a restricted distribution, known only from San Diego County and southern Orange County. Larvae are host-specialists, feeding only on the San Diego sedge (Carex spissa) that is often associated with riparian oak woodlands. Entomologists have expressed concern that the Harbison's dun skipper may be threatened due to habitat loss and degradation. The skipper was once considered a Category 2 species by the United States Fish and Wildlife Service and petitioned to be listed under the federal Endangered Species Act. Currently, it is a covered species in some HCP/NCCP plans in San Diego County. Little is known about this skipper, as the few papers written are limited to describing the general life history and providing a vague distribution. This project is the first phase of a planned comprehensive monitoring program for the Harbison's dun skipper, designed to assist in the development of effective management and conservation practices. We focused on describing the distribution of the skipper, estimating population status and trend, describing habitat requirements of the larvae and adults, and identifying potential threats to the long-term persistence of the species as well as recommendations for monitoring and management. Using herbarium records, information from biologists, and historical Harbison's dun skipper locations, we were able to find San Diego sedge at 38 general locations, primarily on conserved lands. All sedge plants were found in or immediately adjacent to a riparian oak woodland except two small patches. However, both of these locations also had oak woodlands with San Diego sedge present. In many cases, oak woodlands were patchily distributed along a creek and the sedge was only found in those woodlands. We did not find San Diego sedge in or along pools of still/standing water, only in areas with moving water or a dry ravine. We were able to identify 26 historic Harbison's dun skipper localities from museum specimens, peer-reviewed literature, technical reports, and notes from local biologists. Most often, these locality data provided a general description rather than a specific point. Therefore, it can be difficult to know if we were revisiting the same location. Of the 34 locations with San Diego sedge that we surveyed for the skipper, 18 (53%) were occupied which is well below the occupancy rate described by Brown (1982). [consult report for rest of Exec. Summary]