Survey of the butterflies of the Sutter Buttes, California

The Sutter Buttes are a small, isolated mountain group in the center of northern California’s Central Valley. Their location, nearly equidistant between the Coast Range and Sierra Nevada, make the Buttes biogeographically unique. Due to a histoi-y of private ownership public and scientihc access to these mountains has been limited and much remains to be known about the natural histoi^ and ecology of the area. A previous survey of Sutter Buttes butterflies recorded sitrprisingly few species, and was suspected to represent an incomplete record of the butterfly diversity of the area. In order to a.ssess the accuracy of this stirvey and explore the biogeographic relationships of the btttterflies of north-central California, we performed surveys of the btitterfly fauna of the Sutter Buttes. Over two years we performed bi-weekly transects and recorded species presence, abundance, and phenology as well as information about commetn butterfly host plants fotmd there. Utilizing comparisons of transect data from the Coast and Sierra Nevada Ranges we found that the Sutter Buttes butterfly fatma more closely resembles the Central Valley floor fauna than that of either nearby mountain range. Our results also indicate that the Sutter Buttes harbor a significantly depaiqterate butterfly fauna: several btitterfly species that are common at sites in the Central Valley, Coast Range, or the Sierra foothills are not present in the Sutter Buttes. We discu.ss possible reasons for the.se absences, inchiding hre regime, host plant abundance, and nectar availability, and pre.sent