Foraging preferences of the threatened coastal California Gnatcatcher (Polioptila californica) during the non-breeding season

We studied the foraging behavior of the federally threatened coastal California Gnatcatcher (Polioptila californica), an obligate insectivore, during the non-breeding season, a period of reduced survivorship for this non-migratory passerine due to seasonal aridity and the onset of cold winter storms. During the seasonal dry period in fall (October–November), California Gnatcatchers preferentially foraged in fall-blooming shrubs such as coyote brush (Baccharis pilularis), and California brickelbush (Brickellia californica). Upon the onset of the wet winter period (December–January), foraging California Gnatcatchers demonstrated a seasonal shift toward drought deciduous shrubs then leafing out, especially coastal sagebrush (Artemisia californica). Our findings suggest that California Gnatcatchers shift their foraging preferences seasonally to track available food resources. Additionally, our findings point to the value of floristic diversity within California Gnatcatcher habitat to provide year-round foraging opportunities for this obligate insectivore.