Population declines and habitat preferences of the threatened skipper Euphyes vestris harbisoni in southern California

Geographically isolated in southern California and northern Mexico, Euphyes vestris harbisoni is only known to feed on the San Diego sedge (Carex spissa) as a larva. A previous United States Fish and Wildlife Service listing as a Category 2 species demonstrates concern for its conservation but available data was insufficient for a listing determination. The goal of this study was to address biological uncertainties to inform monitoring and conservation efforts. Surveys were conducted in 2021 and 2022 to update the status of populations and evaluate population sizes, and determine habitat preferences by analyzing GIS available environmental data. Skippers were detected at seven of the 17 historic sites visited in 2021, and population sizes are declining at most extant sites. A habitat analysis using GIS available data determined that woodlands with San Diego sedge were more likely to be historically occupied at intermediate elevations with warmer summer temperatures, but wetter sites given this temperature regime. These data identify areas within San Diego County where unknown populations of Euphyes vestris harbisoni are likely to be observed, and where priority should be given to continued monitoring, conservation, and restoration in order to help promote the longevity of the skipper.