Comparative Sublethal Toxicity of Three Neonicotinoids in Red-Winged Blackbirds

Seed-eating birds that use agricultural areas could be exposed to neonicotinoids through several pathways, including ingestion of treated seeds. Previous studies in birds have found sublethal exposure to neonicotinoids can reduce body mass and fat stores, but the underlying mechanism is not clear. We hypothesized that neonicotinoids reduce body mass principally by acting as an appetite suppressant rather than increasing energy consumption. Red-winged blackbirds (Agelaius phoeniceus) were exposed to an oral dose of one of three neonicotinoids at concentrations that could realistically be consumed by seed-eating birds (0, 10, 20, or 30 mg/kg bw of imidacloprid, thiamethoxam, or clothianidin) or were given a moderate or high food-restricted diet (n = 9 or 10 birds per treatment) and were then monitored for 3 days. Imidacloprid caused neurotoxic symptoms and rapid reductions in food consumption and body mass that persisted for >48 h. Food restriction had similar effects on body mass and biochemical indicators of energetic state (plasma triglycerides, uric acid, and β-hydroxybutyrate), which suggests appetite suppression was the main driver of mass loss in imidacloprid-exposed birds. Single doses of clothianidin and thiamethoxam altered food consumption and biochemical markers, but effects were less severe than for imidacloprid, and neither compound caused overt neurotoxicity. This study confirms that acute neonicotinoid exposures can affect behavior, appetite, mass, and energetic state in seed-eating songbirds, with potential consequences for survival.