Ecology of the threatened Harbison’s dun skipper (Euphyes vestris harbisoni) for conservation efforts within a habitat conservation plan

Southern California is a biodiversity hotspot, an area with high species richness and where many species are threatened with extinction. Six lepidopteran taxa are of conservation concern, including three listed on the United States Endangered Species Act. The Harbison’s dun skipper (Euphyes vestris harbisoni) may also have an elevated risk of extinction; however, little is known about its ecology or current status. Due to this conservation concern, we conducted surveys for the skipper to more fully describe its distribution, assess the interannual variation in adult population sizes, and further describe its natural history and habitat requirements (including threats). The known distribution now includes western Riverside County and northern Baja California, Mexico, with the historically reported Orange and San Diego counties. We were able to document 33 historic and/or current skipper locations on public lands and another six historic records on inaccessible private lands. Just over half of the 39 locations were extant populations, about a quarter have been extirpated, with the remainder of unknown status. For extant populations, population sizes appear to be relatively small. We also provide information on efficient monitoring protocols for the skipper. The information obtained from this study is necessary to make data-driven management decisions so that conservation efforts can be effective and efficient.