Type: report

Article abstract: Surveys for Harbison’s dun skipper adults were conducted to assess year to year variation in population size. Field visits were used to document use including plants used for nectar sources, as well as obtain non-lethal genetic samples. A rapid habitat assessment was conducted at each site which included general woodland tree species composition, condition of San Diego sedge plants, and recording potential threats to the Harbison’s dun skipper. We were not able to detect Harbison’s dun skipper adults at all sites, including the canyon south of San Pasqual Academy where it appears the skipper has been extirpated due to wildlife and drought. At four sites (Barrett Lake, Lake Hodges, Skye Valley Road, Sycuan Peak Ecological Reserve), the peak daily number was near or exceeded 10 individuals. At the other sites, no more than four individuals were seen on a single day. There was not a clear relationship between the 2014 and 2016 counts as some were higher, some lower, and some quite similar. In 2016, we observed adults nectaring on sacapellote (Acourtia microcephala) and California rose (Rosa californica), two plant species not previously recorded. The current list of known nectar sources includes 20 species, nearly all of which have white, purple, or pink flowers. Habitat assessments occurred at 23 locations with recent Harbison’s dun skipper observations. These surveys occurred just after the flight season (27 July – 9 August 2016). Oak species dominated the woodlands, with some sycamore and willow trees. The condition of the San Diego sedge plants ranged from nearly all very healthy (green) to all dead. Most of the plants had green leaves with brown tips, suggesting some water stress although this may be typical during the late summer and early fall. The most common threat to the Harbison’s dun skipper was the presence of the goldspotted oak borer (Agrilus auroguttatus). In addition, more than 15 non-native plant species were detected in the riparian areas.