Neonicotinoid exposure in Tricolored Blackbirds (Agelaius tricolor)

There is increasing awareness of the negative ecological and environmental effects of widespread use of pesticides on the landscape. Spillover or drift of pesticides from agricultural areas has been shown to impact species health, reproduction, and trophic dynamics through both direct and indirect mechanisms. Neonicotinoid insecticides are associated with observed declines of insectivorous and grassland birds, and these environmental pollutants are a significant conservation concern for many species that have experienced past or current population declines. Due to the high efficacy of these modern insecticides in depressing local insect populations, insectivorous birds can be negatively impacted by a pesticide-mediated reduction in food supply. Neonicotinoids may act synergistically with other stressors, such as habitat loss, to exacerbate threats to species or population viability. The Tricolored Blackbird is an insectivorous grassland bird of conservation concern in California, USA. Due to the high association of this species with agricultural habitats, we sought to quantify the amount of neonicotinoid residues in Tricolored Blackbird carcasses as a first step in assessing how this species may be impacted by pesticides. Out of 85 salvaged carcasses sampled (N = 24 adults, N = 3 fledglings, and N = 58 nestlings), only two contained detectable levels of target compounds. These were an adult and one nestling that contained clothianidin residue (40 ppb and 7 ppb, respectively); both of these birds were salvaged from breeding colonies associated with dairy farms in Kern County, California. We suggest that further work is needed to assess neonicotinoid exposure of Tricolored Blackbirds in dairy-associated breeding colonies.