Analysis of insecticide exposure in California hummingbirds using liquid chromatography-mass spectrometry

External feather rinses and homogenized whole-carcass tissue matrix from two hummingbird species found in California (Calypte anna and Archilochus alexandri) were analyzed for the presence of nine insecticides commonly used in urban settings. Using a liquid chromatography-high-resolution mass spectrometry (LC-HRMS) analytical method, samples were quantitatively tested for the following neonicotinoids: dinotefuran, nitenpyram, thiamethoxam, acetamiprid, thiacloprid, clothianidin, imidacloprid, and sulfoxaflor. This analytical method was also used to qualitatively screen for the presence of approximately 150 other pesticides, drugs, and natural products. Feather rinsates from both hummingbird species had detectable concentrations of carbamate and neonicotinoid classes of insecticides. Combined results of the rinsate and homogenized samples (n = 64 individual hummingbirds) showed that 44 individuals (68.75%) were positive for one to four target compounds. This study documented that hummingbirds found in California are exposed to insecticides. Furthermore, feather rinsates and carcass homogenates are matrices that can be used for assessing pesticide exposure in small bird species. The small body size of hummingbirds limits traditional sampling methods for tissues and whole blood to evaluate for pesticide exposure. Thus, utilization of this analytical method may facilitate future research on small-sized avian species, provide insight into pesticide exposure, and ultimately lead to improved conservation of hummingbirds.