Type: journal article

Article abstract: The decline in abundance and species richness of insects, including butterflies, have been linked to factors such as habitat loss and climate change. While some butterfly species are increasing, an overall decrease has been frequently observed in both Europe and North America. The objective of this study was to assess trends of butterfly abundances in Mediterranean shrublands of conserved lands in San Diego County, CA, USA. Funding and surveys were focused on the threatened Hermes copper (Lycaena hermes), but the abundance of all butterfly species was recorded. Analyses utilized the annual maximum count (Max Count) for each species at each transect during 2010–2022. The 10 most commonly observed species experienced, on average, a 1.4% annual decline in abundance, and 20 less commonly observed species were, on average, found at 5.9% fewer transects each year. The only exceptions to these declines are species (cabbage white [Pieris rapae], checkered white [Pontia protodice], and white checkered-skipper [Burnsius albezens]) that feed on non-native mustards or are more common in disturbed habitats. The Max Count provided an efficient, robust, and stable population index, that can be utilized to leverage funding for focal species to assess the broader community.