Imidacloprid and chlorpyrifos insecticides impair migratory ability in a seed-eating songbird

Birds that travel long distances between their wintering and breeding grounds may be particularly susceptible to neurotoxic insecticides, but the influence of insecticides on migration ability is poorly understood. Following acute exposure to two widely used agricultural insecticides, imidacloprid (neonicotinoid) and chlorpyrifos (organophosphate), we compared effects on body mass, migratory activity and orientation in a seed-eating bird, the white-crowned sparrow (Zonotrichia leucophrys). During spring migration, sparrows were captured, held and dosed by gavage daily for 3 days with either the vehicle control, low (10% LD50) or high (25% LD50) doses of imidacloprid or chlorpyrifos and tested in migratory orientation trials pre-exposure, post-exposure and during recovery. Control birds maintained body mass and a seasonally appropriate northward orientation throughout the experiment. Imidacloprid dosed birds exhibited significant declines in fat stores and body mass (mean loss: -17% low, -25% high dose) and failed to orient correctly. Chlorpyrifos had no overt effects on mass but significantly impaired orientation. These results suggest that wild songbirds consuming the equivalent of just four imidacloprid-treated canola seeds or eight chlorpyrifos granules per day over 3 days could suffer impaired condition, migration delays and improper migratory direction, which could lead to increased risk of mortality or lost breeding opportunity.